XCOM 2 Alien Analysis: Viper

HP: 7/8/8/10
Armor: 0
Defense: 0
Dodge: 15/25/33/33
Aim: 75
Mobility: 12/14/15/15 (8/16 on Rookie, 9/18 on Regular, 10/20 on Commander/Legendary)
Damage: 3-5 (+2)
Shred: 0
Crit Chance: 0/10%/10%/10%
Will: 50/60/60/60

Immune to Poison.

This isn't... irrelevant, exactly, but it's a lot less relevant than you might expect, particularly in the base game where Vipers are shockingly rare. It's entirely possible to have Vipers basically completely vanish before you get Gas Grenades or Venom Rounds online in the base game, and while they usually show up in the final mission, by that point your crew should be so powerful you don't care about them being immune to Poison outside maybe Legendary difficulty.

War of the Chosen makes the Poison immunity a bit more likely to be relevant. First of all, Vipers are more consistent about showing up in the midgame, where you're liable to actually have Poison infliction and still have weak enough weapons that killing them is a bit of an obstacle. Second, Hunter's Instincts has been nerfed, so Rangers in particular aren't so reliable about trivializing Vipers. (A Shard Gun backed by Hunter's Instincts does 9-11 damage on non-crits in the base game, ensuring a kill outside Legendary, where it still kills on 2/3rds of non-crits if we ignore Dodge... which we should. In War of the Chosen, that's instead 7-9 damage, potentially leaving a Commander Viper alive, and demanding a crit or other boost to ever kill a fresh Legendary Viper) Third, Skirmishers and Reapers have poor per-hit damage, where negating the damage boost from Ammo can have a more dramatic effect on survivability.

Fourth, and correlated to their greater tendency to appear in the midgame, is that it's more normal to see pods with multiple Vipers in War of the Chosen. This makes it a lot more likely they'll end up benefiting via a buddy using Poison Spit without it being an issue for the other Viper(s).

Also, fifth is the existence of Beta Strike. A Beta Strike run is a lot more reliable about really feeling that Poison protection, and the base game doesn't have any settings to increase its relevance aside Legendary difficulty being less egregious about vanishing Vipers quickly.

Poison Immunity's still not very relevant in War of the Chosen, mind, but it's more relevant, which is nice.

Tongue Pull
Can pull humanoid enemies from 3-12 tiles away, dropping them orthogonally adjacent to the Viper on a successful hit. This is a regular accuracy check, affected by height and Cover and the Viper's own current Aim, with +20 to base accuracy. This consumes one action point and does not end their turn if it misses. On a successful hit, the Viper immediately initiates a Bind on the target even if they have no action points remaining, and ending their turn if they have do have any action points remaining. 1 turn cooldown.

Surprisingly, Bladestorm will actually cause a soldier hit with the tongue-pull to take a swipe at the Viper after they've been pulled, potentially preventing a Bind! (By killing the Viper)

On the other hand, a soldier being pulled in by a Viper is actually treated as having moved for purposes of enemy Overwatch triggering. The Overwatch shots are still less dangerous than if the enemies had just taken shots, what with no crit chance and worse accuracy, but it can still be an unpleasant surprise to have a couple enemies decide they don't like their hit chances, go into Overwatch, and then instead of you getting to negate their Overwatch a Viper pulls someone and they get shot.

The game also doesn't cope very well with Tongue Pull hitting a Bladestormer, animation-wise, as a Bladestorm interrupt will cause the soldier to visually stop roughly halfway between them and the Viper to play their attack animation, even though their real position is adjacent to the Viper. And if the Viper survives the Bladestorm, it will promptly visually slide over to the soldier's displayed position, which can get really confusing when you try to save your soldier, if you don't realize the glitch is happening or do realize it but have already forgotten the Viper's real position.

It's too bad War of the Chosen didn't correct this animation error...

Anyway, thanks to the +20 accuracy on Tongue Pull, it's alarmingly reliable. Against a target in the open, it's a 95% chance to hit, when the vast majority of enemies can't achieve that level of accuracy without high ground and/or external boosts like Mark Target. Against a target in Low Cover, it's still a 75% chance to hit, at bare minimum, so you should basically assume any sufficiently close Viper is going to succeed on the Tongue Pull if you don't have other mitigating factors at work (eg Smoke Grenade, Suppression) and don't have everyone in High Cover. It does not benefit from the Aiming Angles effect, though, so High Cover is reasonably reliable protection from it, enough so that a Viper faced with a lone soldier behind High Cover is liable to either attempt a partial flank and fire or go into Overwatch, instead of attempting a Tongue Pull.

The maximum range is an important limitation to keep in mind, and it can be useful to count tiles if you're unconvinced you can kill a Viper and are trying to figure out its likely course of action. The minimum range, meanwhile, is something you could be forgiven for not realizing is a thing, because in most situations where a target is too close that will just result in...

Binds an adjacent humanoid enemy, doing 2-3 damage on initial activation and on each following turn. The Viper and their victim cannot act until the Viper takes damage or their target dies or falls Unconscious, with the exception that a Viper may elect to end the Bind on future turns as a free action. 1 turn cooldown.

... a manual Bind.

The +1 damage on Bind is a 25% chance, for reference. Also note that the ability to end a Bind manually is only relevant for player control purposes: the AI will never end a Bind of its own volition.

Further note that while a Viper initiating a Bind will remove the Viper's Cover icon, in actuality they're treated by the game as being in the tile they started the Bind from for the purposes of calculating Cover. As such, if they initiate a Bind from High Cover, they're still going to be difficult to hit if you don't flank them or smash that Cover, even if they're against a freestanding pillar where they visually have no possibility of Cover post-Bind. Don't give Vipers standing in High Cover an opportunity to Bind someone from their current position if you can avoid it.

A manual Bind can't miss, unlike Tongue Pull, and by a similar token Bind doesn't care about special blocks: a Templar currently Parrying or another soldier benefiting from Untouchable will automatically evade a Tongue Pull attempt, but a Viper slithering up next to them and going for the Bind will succeed just fine. Tongue Pull is the usual way for someone to end up Bound, but if you eg have a Templar Rend a Viper and then Parry, the Viper is more or less guaranteed to Bind the Templar, not caring that you used Parry.

I say 'more or less guaranteed' because Bind has the unusual quality of only being allowed to target orthogonally adjacent targets. So if, for example, you trigger a pod, have your Templar Rend the Viper, and you have Tactical Analysis slotted in so the Viper only has one action point, the Viper may be unable to initiate a Bind on the Templar by virtue of the Templar being diagonally adjacent and the Viper lacking the action points necessary to move and then Bind. A non-obvious implication of this is that it's generally more useful to melee a Viper from a diagonal instead of an orthogonal, as meleeing them from a diagonal will force them to move if they want the Bind, and Vipers heavily prioritize going for a manual Bind on targets within the range they could move next to while still having an action point to spend on Bind. In many cases, attacking from a diagonal will thus lead to the Viper moving to a space in the open before initiating the Bind, making it much easier to take out, where attacking it from an orthogonal will lead to it remaining in the Cover it was probably standing in.

Bind itself is something of a mixed blessing. It has low damage, and Bound units are almost always ignored by the majority of enemies, so sometimes a Bind can be what prevents a soldier from dying (eg they end up Bound instead of sliced up by a Chryssalid), but it's also one of the few sources of guaranteed damage the AI has, and one of the few the AI is extremely aggressive about using. Particularly early in the game, it's easy to end up with a soldier chipped to death by Bind because you keep rating the Viper as a low priority and Grazes keep it alive for longer than you expected and three or five turns later you've got a dead soldier.

If you know how to plan around it, it generally contributes to Vipers being less of a threat than most enemies, letting you perform seemingly-reckless plays in complete safety because the soldier you left exposed is going to be Bound for mild damage and then ignored by all the other enemies instead of killed. It's actually a bit f a recurring trend that understanding AI quirks can lead to you planning around them using an ability in a particular way that you've arranged to be least problematic for you, but Bind stands out because it's so easy to manipulate and can be used to outright protect a soldier from other enemies. Got a soldier at 5 out of 16 HP, who you're worried will be instantly killed by an Elite Trooper or whatever, and you can't get everything killed and/or disabled? Then it's actively a good idea to get that vulnerable soldier in a position to be Bound, since it can't kill them and will ensure other enemies ignore them. That's... a bit of a perverse dynamic.

Fortunately, it's not as bad as you might fear, as Vipers are only temporarily guaranteed to be pod leaders, and as I've noted before pod leaders always go first out of their pod. Still something to keep in mind when a Viper is a pod leader in the mid-to-late game, but it won't crop up constantly across runs.

Anyway, Bind also has a scaling factor akin to Seeker Strangulation doubling its damage with each successive turn, though I haven't tested this mechanic enough to be confident in the details. (Hence why I don't have them listed in the non-italics portion above) I suspect it's doubling the damage each turn, just like Strangulation, but I rarely let Vipers sustain a Bind, and outside Beta Strike soldiers die too quickly anyway, making it difficult to be sure of the exact formula. It might just be +100% of the base damage per turn, for example.

Animation-wise, Bind is kinda... dumb. Design-wise, it's sensible for Bind to be a mutual disable, where the Viper can only focus on the Bind, but the animation doesn't really sell this, with the Viper's hands remaining free, and indeed its entire upper body is sufficiently up and out it really ought, logically speaking, to be able to turn about and shoot at other people, or at least to point its firearm at its victim and shoot them in addition to the Bind, not to mention spit poison. This is a pretty stark contrast to Seekers Strangling people in Enemy Within, where their design naturally answered the question of why they couldn't take shots while Strangling, and the only problematic question was the part where they were robots and so presumably could've been constructed in a way that avoided that issue. And even that wasn't much of an issue, since the Seeker's Plasma Pistol is clearly more a backup weapon than anything else: it was perfectly believable that the in-universe manufacturers considered blocking Plasma Pistol usage during a strangle to not be a real flaw.

Regardless, it makes me wonder if the Viper was supposed to be able to fire while Bound, that capability got cut, and the animation didn't get modified appropriately, or if the animation not making sense was just... fundamental. Either one seems plausible.

Poison Spit
Spits Poison into a large area, potentially Poisoning units caught in the immediate blast and also Poisoning any units that pass through the clouds. This consumes one action point and does not end their turn. 4 turn cooldown.

Curiously, Poison Spit has an entry in the config files indicating it's supposed to do 3 damage and ignore 1 point of Armor. In the actual game, though, it just fills the area with Poisonous gas and immediately Poisons everything in said area that isn't immune. (Well... usually everything. Sometimes individual soldiers don't get affected for no clear reason) I assume at some point in development Poison Spit did immediate damage, and the config file just didn't get cleaned up before release to fit the removal of this mechanic, or something of that sort.

The Poison cloud itself works just as it does when you use Gas Grenades, aside that Gas Grenades have immediate damage+Shred: afflicted units take 1-3 damage a turn, their Mobility is reduced by 4, their Aim is reduced by 30, and the Poison can spread to adjacent units, all while lasting 4 turns. The gas can't co-exist with Acid clouds or fires. Etc. The spreading potential is a lot more relevant when applied to your soldiers, mind, since the player isn't necessarily as obsessive about avoiding clumping and in fact has a few mechanics -like Solace and Bonds- that actively encourage clumping. But mechanically, it's the same.

One bit of design I have mixed feelings about is that the AI doesn't 'see' Poison immunity when deciding whether, and where, to launch Poison Spit. On the one hand, it would be a bit frustrating from a realism standpoint for the AI to 'see' Medikit or Fortress-based immunity (Items show on soldier models, but Medikits aren't blatantly obvious at a glance, and Fortress is invisible unless actively protecting the soldier), as well as slightly reducing the real benefits of those protections. On the other hand, it's really just kinda dumb that SPARKs and Hacked robots are also cases a Viper will fail to account for; this is yet another reason why SPARKs are very front-loaded in quality, because an early SPARK will frequently provoke Vipers into completely wasting their turns, where there's no later enemy with an equivalent issue. (Particularly in the base game, where Purifiers don't exist) In any event, be aware that having Widespread Poison immunity on your squad can make it a lot more acceptable to ignore a Viper for a turn.

This is because Vipers have one of the more rigid, predictable AI behavior sets, making it unusually easy to play around them, and making their blind spots much more consistently relevant. So let's talk about their procedure.

First a Viper will check if any hostile is both next to it and susceptible to Bind: if such a thing exists, they immediately Bind without further thought, unless Bind is unavailable due to eg Disorientation, in which case shooting and moving are their only options and you can ignore most of this. Then a Viper will, if it has two action points, check if there's anything within range to move orthogonally adjacent that is susceptible to a Bind, and if there is it's basically guaranteed it will do exactly that. (There's been a handful of occasions I've seen a Viper pass such up, but it's really rare, and I'm not entirely sure what prompts deviation from this) If neither option is available, the Viper will check if there's anything it can Tongue Pull, and if so it will attempt that, preferring to go for whatever target is most likely to be hit. On a success, it of course Binds and the turn is done, while on a fail it searches for if there's a good Poison Spit target.

This is the point at which a Viper finally becomes less obviously clockwork, as a Viper prefers to hit multiple targets with a Poison Spit and prefers to use its firearm if it can't get multiple targets but other contextual factors can eg lead to a Viper deciding to Overwatch even though it has a decent Poison Spit target (eg the 'don't stack area of effect stuff' bit of overall AI overrules them) or taking a shot over a Poison Spit because the shot is unusually good.

Nonetheless, the point here is that, if anybody is in Tongue Pull range, the usual outcome is that the Viper will either successfully Tongue Pull them, or fail on the Tongue Pull and immediately follow up with a Poison Spit. And if nobody is in Tongue Pull range, and they can't get a flank with one move, they'll usually move and then Poison Spit. So Poison immunity is really reliably helpful, because it's very strongly their preference after Binds.

This also ties back into why SPARK immunity not registering is... kinda dumb... in that SPARKs can't be flanked, can't be Bound, are immune to Poison Spit, and have enough innate Defense to make the Viper unhappy with its hit chances on regular shooting, and the final result is that unless there's a confounding factor like the Viper having high ground or the SPARK being Marked by an Officer, Vipers are extremely prone to reacting to a nearby SPARK by trying to back up to avoid being flanked and then hurling a completely useless Poison Spit at the SPARK, often even when no other units of yours are in the targeted zone. If you're a big fan of Strike on SPARKs, you're liable to see this behavior quite readily, even aside the possibility of trying to deliberately leverage it.

Even if you keep the SPARK further back, it's still entirely possible to end up with a Viper advancing and then hurling a Poison Spit at your SPARK. Vipers really like Poison Spit.

Fortunately, Vipers are an uncommon enough enemy overall that this doesn't usually dominate runs, but it's still problematic design, and I'm sad that even into War of the Chosen Viper AI wasn't adjusted to account for SPARKs.

Less dumb but also moderately abusable is if you get lucky enough to get a Templar with Fortress, where of course you've taken Parry. Such a Templar can Rend something in the open, just far enough away from a Viper that the Viper can't slither up to it for a Bind, and this will very reliably result in the Viper firing off a Tongue Pull (That gets Parried) and following up with a Poison Spit. (That accomplishes nothing because Fortress) This requires relatively precise placement and a good sense of how far Vipers can move, but if you get all that it's shockingly reliable -they won't Tongue Pull and then shoot, bizarrely enough, even on a Templar in the open.

... and I've already covered how Vipers don't 'get' Lost.

Vipers really needed their AI reworked in War of the Chosen...

Overall, Vipers are like a hybridization of Thin Men and Seekers; a poison spit attack and Poison immunity like Thin Men, combined with Seeker-esque having a melee attack that disables the target but involves turn commitment of the attacker. I'm a little surprised Vipers weren't also given Leap. What, would them using their tail as a spring have been too silly for this game's tone? I'm also surprised they didn't bring back the 'explode into Poison cloud' mechanic, and a little disappointed too, given that would've been a lot more interesting a mechanic in XCOM 2 where the player has melee attackers. It was, admittedly, more obnoxious than anything else on Thin Men, but XCOM 2 has removed a lot of why it was obnoxious rather than an interesting threat. So it feels like a missed opportunity.

In any event, Vipers are a weird unit that I think needed better tuning. The game approaches them as an early-ish game unit, with durability comparable to a Sectoid if we ignore Dodge and the lack of a weakness to melee, and fairly poor offensive capacity, but it takes them long enough to actually show up in most runs that they're basically understrength compared to their peers. They're also not as strongly oriented as some units are to filling a 'complicate the fight' role; the Poison can be irritating for biasing the RNG away from you, but it's not the sort of thing that gets more dangerous by having a Viper operating alongside other units, it's just generally inconvenient. Bind is a little closer to a complicator ability, since it means you need to burn a turn on freeing a soldier by hitting the Viper, and probably a lot of players don't realize it's perfectly possible to toss explosives at a Viper without hurting the unit they're Binding, but... Bind can actually be a good thing for you, as its damage is very weak and normally enemies will ignore your Bound troops in favor of shooting at other soldiers, potentially saving the Bound soldier's life. Unlike Seekers there's nothing about how Vipers are designed that makes them likely to go after an isolated soldier, either, unless one assumes players habitually hurl melee attackers far from the rest of the squad.

So... what are Vipers really supposed to be doing as an enemy? They're not a straightforward combatant like eg ADVENT Troopers, but they're also not a complicator like a Codex is. They're in an awkward middle space where they're not liable to straight-up kill people but you also largely don't care about what they're doing because they can't make a tricky situation particularly more problematic.

War of the Chosen accidentally makes them a bit more problematic, as Lost won't ignore Bound troops and in fact will often prioritize them over attacking the Viper that's Binding them, so in missions that happen to have Vipers and Lost you can end up losing a soldier unexpectedly, but that's... clearly not intentional behavior and is a fairly unlikely, specific situation. And not an interesting form of threat, either.

It makes it all a bit weird and frustrating that Vipers were clearly something the team was fairly fond of, given that Alien Hunters puts a lot of attention on Vipers.

On a completely different note, one non-obvious, kind of bizarre implication of the game's design worth discussing in relation to Vipers is how Dodge's impact on combat lowers as the game progresses.

You might intuitively expect it to be greater, since a Graze halves damage. Dropping an 8 to a 4 is twice as much damage lost to a Graze, right? But this doesn't really matter. Ratios and how many shots it takes to kill things is what matters.

Ratios might also seem a strange thing to bring up, since halving damage is inherently proportionate; this isn't like how 3 Armor is subtracting half damage if the incoming attack is 6 damage, but only subtracting a third of the damage if the incoming damage is 9 damage, or subtracting three-quarters of the damage if the incoming attack if 4 damage.

However, the key thing here is that Grazes halve damage rounding down.

The Rifle is the best weapon to use for illustrating the point, as it's the most impacted of the primary weapons by this consideration, with the weakest damage and the greatest proportion of its possible damage rolls on odd numbers where rounding down applies. A Plasma Rifle does 7-9 damage; if it rolls 8 and Grazes, it loses exactly half of its damage. If it rolls 9 and Grazes, it loses 5 damage, which is slightly greater than 55% of its damage; virtually indistinguishable from rolling a Grazed 8 in terms of lost damage. And lastly if it rolls a 7 and Grazes, that loses slightly over 57% of its damage; pretty close to 60%.

Overall, though, those numbers work out to a Graze being 50% damage lost or so close you literally only care if the Graze causes eg a Viper to survive with exactly one hit point where it should've died.

A Conventional Rifle, though, is hit much harder by this. A Grazed 4 is a simple 50% loss of damage, of course. A 5 that Grazes has lost 60% of its damage; that hurts, but is only slightly more than a low-roll Plasma Rifle Graze. No big deal, right?

A three that Grazes, however, loses two-thirds of its damage.

Further note that the average or expected damage for a Conventional Rifle is 4 damage. A Grazed 3 is a loss of 75% of the damage you will usually expect to do with a hit. With the Plasma Rifle, your average or expected damage is 8, and a Grazed 7 doing only 3 damage is 62.% lost; hurtful, but not nearly as hurtful as the equivalent situation on a Conventional Rifle.

(This is also ignoring that Grazing overrules crits, and crits become a smaller proportion of damage as you progress, on every weapon. I don't want to lay out that whole mess, just keep in mind it contributes to the point I'm driving at)

To put things in more concrete terms, let's say we're dealing with a Commander Viper. Our crack squad of six Specialists wielding Plasma Rifles will normally kill the Viper in 2 shots, or even 1 if they get a crit. If a malevolent deity curses them to always do the lowest possible damage on a hit, including always Grazing, forcing them to do 3 damage per shot, they will take... 3 shots to kill a given Viper. That's only 50% more shots than they normally expect to take, and three times what it would take compared to a crit. Undesirable, but a full squad of Specialists is still going to kill two Vipers per turn.

If we switch to saying our crack squad of Specialists is an unfortunate squad of Rookies with Conventional Rifles shoved into their hands and told to die for the Earth, preferably taking some Vipers with them, the no-Graze result is that it will take them 2-3 shots to kill a Viper, with a crit merely ensuring they take two shots instead of three. Then a malevolent deity curses our poor Rookies, and now it takes eight shots to kill a Viper. That's four times as long as the best case scenario of 2 shots to kill, and even compared to the worst case of three shots it's still more than twice as long. Our cursed squad of six Rookies can't even kill one Viper in a turn!

This means that Dodge-based enemies have a much swingier effect on combat early in the game than later. Late in the game, a Viper who Dodges frustratingly often is a problem, but not a severe problem. Early in the game, you can do literally everything perfectly and have nobody miss a shot and still have Viper Dodges completely screw you over.

Now, realistically you're not using only Rifles, but the other core classes will take 1-2 hits to kill a Viper, and will take 4 with constant low-damage Dodges, and switching to beam-tier weapons switches those numbers to '1-2 shots normally, 2-3 shots if it's all low-roll Dodges'. The Rifle is the most dramatic of the base-game examples (Skirmishers and Reapers are in similar boats, it should be noted, since at Conventional they can roll 3 damage), but this is broadly true of Dodge mechanics.

Thus, Vipers tend to be memorably frustrating, more so than later enemies that also have high Dodge, which is all-around weird. I really hope the devs do something to escape this bit of strangeness in XCOM 3, whether overhauling the Dodge stat, doing away with it entirely, keeping track of fractions of damage/HP, or raising base values to effectively keep track of fractions. (That is, if a Rifle did 30, 40, or 50 damage, while ADVENT Troopers had 40 HP, and extend these rules to all HP/damage values, then a Graze on a low-roll Rifle shot would do 15 damage, with two such Grazes adding up to 30 damage, and that's all the same as instead tracking 1.5 damage in the current scale)

Also, while we're on Dodge, it turns out it doesn't work the way I thought it did when laying it out for the PCS post, though I... still am not entirely sure how it actually works, because the explanations I've seen online don't jive with Extended Information's predictions nor my actual experience in playing the game.

The explanations I've found when going digging come back to the 'one die roll for accuracy+crit' mechanic and indicate that Dodge is rolled into this same mechanic, but 'filling in' from the top and overruling a hit result. This explanation would, among other things, imply that the first point of Dodge is literally worthless, and more generally imply that low-accuracy shots don't have to worry about Grazing unless Dodge is extremely high.

This is... clearly not correct, as eg Advanced and Elite Officers have 15 Dodge and yet can be Grazed by shots that had less than an 85% chance to hit, but something unintuitive is happening with Dodge. I'm still digging if I can figure out/find out what's actually going on.

Returning to Vipers...

As a hypothetical Domination target, Vipers are poor. In the first place, they're primarily an early-game threat, and in the base game in particular you're quite likely to have more or less no opportunity to Dominate one, but in the second place they're... typically not very useful Domination targets. Fragile, soft-hitting by the time you're liable to have Domination, and their special abilities can be useless if the rest of the map is made up of non-humanoid enemies that are immune to Poison.

They do have some edges. Poison Spit and Bind gives them more ability than many enemies to 100% reliably contribute to a fight, the fact that most enemies will virtually never reach 100% accuracy means their high Dodge stat will basically never be neutered when conventional attacks are in use, and they have surprisingly high Mobility, making them better able to flank than you might expect.

But it requires an improbable confluence of events for them to be liable to be a better Domination target than, say, a Trooper. And the further you get in the game, the more unappealing they become, tending to be surrounded by better options, and being hurt by how the late game increasingly adds in enemy types Vipers are terrible against: if you had Domination at the beginning of the game, right when Vipers are first showing up, they're the only thing immune to Poison around, and it's just them and Sectoids for being invalid Bind/Tongue Pull targets. (Okay, and Chosen and Turrets, but they're both weird and don't substantially change my point) They'd be pretty good Domination targets under those conditions.

Once everything is in rotation, though, more than half of everything you can encounter is immune to Poison, immune to Bind and Tongue Pull, or both, making it distressingly likely a Dominated Viper will be little more than a fragile distraction with poor damage output.

All that said, it is possible to get Domination early enough they're actually a pretty decent option. If you beeline to Psi Operatives and end up getting Domination as literally the second ability of your first Psi Operative, Dominating a Viper might actually be your best option. So don't completely dismiss the possibility.

Vipers are weirdly rare if you don't have Alien Hunters on so the Nest will prop up their numbers, which can end up fairly frustrating since you need their corpses for Battlefield Medicine, and also need them to make Nanomedikits if you don't stockpile ahead of Battlefield Medicine completing, all of which of course requires burning a corpse on their Autopsy first. Since there's nothing forcing them to show up in decent numbers in missions you'll collect the corpses in outside the Nest, it's entirely possible to end up with too few corpses to perform the Autopsy+Battlefield Medicine across your entire run. So don't sell them!

This comes down to Vipers having a unique position in how spawn stuff is handled; they're an early-game enemy, but unlike other early-game enemies they neither have higher-tier forms to keep them relevant nor do they get commonly attached to any later-game enemies as a supporter. (Where eg Sectoids tend to be attached to Gatekeepers, even though they share with Vipers being an early-game enemy with no elite form) Worse, they're not so early-game as to be allowed to show up in the beginning-of-game missions, which are disproportionately prone to being mission types where you get to collect the corpses. They actually have a fairly narrow window where they're semi-common, and then basically go away entirely.

Notably, there are other enemies that tend to stop appearing in late-game spawn tables... but are commonly found in Retaliation missions when they are around, which occur at a relatively regular pace and always let you loot all the bodies if you win, all but ensuring you'll get a decent supply of bodies. Berserkers, Chryssalids, and arguably Faceless all fall under this banner. Vipers don't benefit from something equivalent.

On the plus side, Battlefield Medicine is more a nice-to-have than a must-have (For one thing, if you exclusively use Specialists for medical duties just upgrading your Gremlins is already upgrading your healing), so it's not nearly as problematic as it could be, but still. I kind of wish War of the Chosen had done something like introduced a late-game Viper variant. Something to make it a little more consistent that you acquired their corpses eventually. I doubt it's really intentional that you can get screwed out of Battlefield Medicine in particular. War of the Chosen did at least make them less prone to completely vanishing past the early game, but Vipers are probably the early-game pod leader enemy that suffers the most from player advancement. Early game Vipers are a moderate threat. Late game Vipers are a relief, clearly less threatening than... basically anything else that could be in their slot, which is really not how enemy generation should function, and contrasts with eg Sectoids staying relevant through Mindspin if you're careless.

Some manner of elite Viper variant that dropped a regular Viper corpse would've been a more elegant solution to the issue.


An amusing oversight: when you first encounter a Viper, your support staff will talk about Vipers being the true form of Thin Men, and Bradford in particular will remark that there's no need for them to hide because the aliens don't need an infiltrator unit anymore...

... when the game is designed so you'll have your first Retaliation mission before you encounter your first Viper, and so in a typical run where you take on every mission and so on, you're guaranteed to have already seen Faceless, which are a new infiltrator unit. So Bradford saying this makes absolutely no sense, for completely design-avoidable reasons: just make Vipers show up earlier, or the first Retaliation mission show up later.


For whatever reason, Vipers are something of a vortex of writing-related issues like this. Usually when I'm mentioning storytelling issues with enemies, it's to do with unclear and improbable worldbuilding, or that the enemy has connections to central plot elements that never get properly explored. Vipers instead have multiple straight-up incorrect things attached to their writing. I'm not sure why.

Second notable error: during the Viper-first-sighted intro discussion among your support staff, Tygan describes Vipers as revealing their 'true form' as a 'wholly reptilian species'. This has two layers: the first layer is the relatively scientific one, which is a problem because Tygan is our resident Scientist Character. Said layer is that Vipers are aliens, and so talking about them as if they're related to an Earth-creature classification is deeply wrong.

But okay, let's ignore that and assume Tygan is using this wording in a descriptive sense, observing how Vipers look suspiciously like Earthly cobras made huge and given arms. I find this strange of Tygan to do, given most of his characterization, but sure. This still runs right into layer two: that as our resident Scientist Character Of No Particular Specialization Or Discipline, Tygan really ought to know that breasts -which Vipers have- are exclusive to mammals, to the point that the word 'mammal' is literally derived from the Latin word for 'breast'. Frankly, I'm pretty sure most people know that mammals have mammaries and everything else doesn't, but the resident Scientist Character being the one to get this wrong makes it particularly absurd, where I class it as flat-out a writing mistake. (As opposed to believably an in-character error) Vipers aren't 'wholly reptilian', not in a technical sense (They don't have an Earthly lineage, so they're not related to any of our reptiles), nor in even a colloquial sense. (Reptiles don't have breasts, Vipers do)

Third notable error: in the Autopsy, Tygan jumps to the idea that all known Vipers being female might be an Ethereal form of population control.

As the in-universe intended explanation, this is... functional. I don't like it for reasons I'll return to later, but my primary issue isn't that the developers intend it to be true, it's that Tygan jumps specifically to this explanation for the observed phenomenon of 'nobody on Earth has seen a male Viper'. (Outside the Viper King, once Alien Hunters came along, but that's beside the point) There are a lot of alternative explanations available for 'we've never seen a male Viper/only seen one by virtue of Vahlen doing Mad Science', and there's really no reason for Tygan to drop this explanation and no other in beyond 'the devs thought this up as the explanation, used the Autopsy report to deliver the explanation to players, and didn't think about it any further'.

If I was a Scientist Character in the dark, dystopian future of XCOM 2, here's some theories I would've come up with that could explain the observed data of 'no human has seen a naturally-occurring male Viper on Earth'.

Scenario 1: Eusociality

I think most everyone on Earth is aware of ants, and most people are aware of bees and termites. If you've ever cracked open a biology textbook for even ten minutes, odds are good you've read about eusociality (Maybe not explicitly referred to with that term, but whatever), where these species aggregate into teeming hordes of tightly-allied workers and warriors, even if you never explicitly recognized that these eusocial species are doing that. (Frankly, though, you probably figured out the basics of eusociality on your own without needing a textbook, just by watching an ant nest or some such in childhood or similar)

Odds are also good if you've ever read such a book -or online article, nowadays- for any period of time at all that the author has gone out of their way to rapidly point out that the most well-known examples are heavily female, where the worker and warrior classes are all female and male members are limited to a bare handful, in many cases only produced at specific time periods just before they're needed.

If you're slightly more interested in biology -or just like reading Weird Science magazines and whatnot, or just read literally the Wikipedia link above- odds are also good you're aware that there are, in fact, eusocial species that aren't ants, bees, or termites. Indeed, some of them don't even have carapaces.

So armed with that elementary-school-level of knowledge, why doesn't it occur to Tygan that Vipers might be a eusocial species, presumably with their nests/hives/whatever-you-want-to-call-them simply placed somewhere offworld so there's no risk of human dissidents blowing them up? This neatly explains why all Vipers have one apparent gender, as humans would only ever be seeing the soldier or worker caste, never the queens or males.

But okay, fine, our Resident Scientist Character is incapable of thinking of the possibility that literal aliens might be eusocial. I dunno, maybe he gets stuck on the idea that they look like reptiles and no reptile is eusocial. (That humans yet know of as of this writing) He's human, and scientists can make perfectly ordinary dumb assumptions of this sort.

But what about...

Scenario 2: Parthenogenesis

This is admittedly semi-obscure, but if you can't be bothered to read the Wikipedia link, parthenogenesis is, for the purposes of this post, a species maintaining itself through natural semi-cloning, no need for males to get involved. Females simply induce eggs to start growing on their own.

There are reptiles that can do this, among many examples capable of such. The reptile in question can never produce adult males of its species, leading to a mono-female species. Sounds a bit familiar, doesn't it?

So... why doesn't our resident Scientist Character come up with this as a theory?

And to be completely explicit, notice that this is a theory that ends up with Vipers being mono-female, where said mono-female-ness has zero possibility of functioning as a form of population control.

The especially strange thing about Tygan's failure to bring up parthenogenesis is that the internal name for Chryssalid Poison is 'Parthenogenic poison'. Somebody on the development team knew about this idea and understood it will enough to creatively apply it in a context it's actually correct in. Normally I might assume literally nobody on the team knew of this semi-obscure concept and that was the issue, which would be disappointing, but nobody knows everything, and even a large team is going to have things nobody on the team knows. But... that can't be the explanation in this case.

But wait, we're not done yet!

Scenario 3: Hostage Vipers

I've touched on a similar idea with the eusociality theory, but part of why it's just baffling that everybody in-game assumes Vipers are actually mono-female and jumps to an explanation involving genetic engineering to control their population...

... is that there's a blaringly obvious, much more prosaic explanation available, of male Vipers being kept hostage offworld.

This covers the population control element of the theory just fine, too, if the characters in-universe are unhealthily attached to the idea that the Ethereals are engaging in population control. Which isn't even particularly unreasonable for them to latch onto, honestly, given that XCOM 2 heavily implies Earth's population is substantially diminished and the Ethereals are vanishing animals and otherwise undermining human ability to function if they're not under the Ethereal thumb. Point is, no need to assume Vipers are mono-female to generate a population control theory.

But okay, maybe two blaringly obvious and one semi-obscure explanation failed to enter the skulls of our entire support staff. Maybe- nope, still not done.

Scenario 4: Aliens Be Alien

Vipers are aliens. They are creatures from another world, whose resemblance to Earthly cobras is most likely coincidental in-universe, or maybe a form of convergent evolution. By a similar token, the fact that Vipers all apparently have breasts like a specific sub-set of species on Earth have going on with females... doesn't necessarily mean anything. It could just as easily be that every Viper we see is male, and the structure on their upper torso just happens to look like breasts contained in a bra. Or that they're a random mixture of both, and the breasts (Or 'breasts') are unrelated to whether they're male or female.

This is especially frustrating given that in their Thin Men incarnation Vipers were, from a human-expectation visual standpoint, uniformly male. Why would you assume that the current Viper incarnation was necessarily any more representative of their true form than the last one? Even if we go with the fictional meta-pattern where human visual signaling of 'male or female' is magically conformed to by literal aliens, then either Vipers were blatantly transgressing that pattern in the last game and we have no reason to trust their current form isn't also transgressing that pattern, or... there are Viper males, Thin Men were all male Vipers, and the scenario isn't 'there are no male Vipers', but rather is 'we don't know what they're doing now that they're not being Thin Men'. (Which is a bit of a convoluted, mildly arbitrary theory, note)

To be honest, I find it frustrating I have to raise any of this, because the fact that I have to is itself a byproduct of XCOM 2's extremely strange, confusing decision to insist that X-COM as an organization is thoroughly ignorant of the alien overlords and their alien enforcers. The Ethereals are supposed to have been more or less in control for nearly twenty years, with aliens walking the streets openly for most of that. Normally I'd assume that everyone on the team was assuming Vipers are all female because this is a common-sense fact everyone knows because Vipers have been hanging out with humans for more than long enough for basic information to have trickled out to more or less every human on Earth, and the only unknown part is why they're all female, where presumably the Vipers -and everyone else that knows- is being tight-lipped about the info.

... but XCOM 2 persistently insists on structuring itself as if your support staff are thoroughly ignorant of all aliens, only slightly less so than the Commander who is at least justified in being ignorant of all this due to being in a stasis tube for the past twenty-ish years. Your support staff are allowed to have a superficial level of knowledge of returning aliens, but multiple plotpoints and random Avenger conversations reiterate the idea that your support staff -that the X-COM organization as a whole- doesn't know the alien language, knows nothing about the cultures of the assorted aliens, knows nothing about major, obvious elements of their biology...

... so I can't take the common-sense approach and assume 'Vipers are all female' is just info in the metaphorical air, known to everyone because the Vipers themselves make it known pretty readily. Indeed, this issue is pretty core to why I bother to bring up all these possible explanations at all. If the game took it as more of a given that your support staff has basic common-sense info about most aliens -there's a handful like Faceless that are supposed to be actual secrets, so fair enough about being ignorant on them- then I'd tend to assume Tygan was dismissing these other theories because nobody had ever heard a Viper talking about off-world males, off-world nests, etc, and in turn assume that Tygan was inclined to assume we'd have heard evidence of these possibilities if they were what was going on.

But the game doesn't. Your team has gathered near-zero information about their oppressors in the last twenty years, somehow.

... I seriously don't get why Vipers in particular have these writing problems. There's writing problems with other species/elements of the game world, but nothing so obviously wrong as with Vipers.

Moving on though, let's... return to the point that I don't like 'Vipers are mono-female as a form of population control' explanation, even though it's functional as an in-universe explanation.

In some sense Vipers are actually a callback to the original Snakemen, more so than I suspect the average player realizes. While Snakemen are named Snakemen, the Snakeman autopsy in classic X-COM reveals that Snakemen are filled with a ton of eggs, telling us that they're actually Snakewomen and heavily implying they reproduce by parthenogenesis. Vipers being a mono-female snake-like species is, by certain metrics, actually a fairly one-to-one repeat of Snakemen.

But... why doesn't this extend to Vipers reproducing via parthenogenesis? Why make it a form of population control? Why cleave so closely in some ways, but then take Snakemen and turn them into Sexy Snake Ladies who have no males because Sinister Ethereal Activity rather than... you know... the aliens being alien?

This touches pretty directly on one of the things I really disliked about the prior game, and that still frustrates me a bit in XCOM 2: that Firaxis keeps taking these wild, alien beings from far-off worlds and then crams them into a more ordinary, less alien framework. This gets reflected in word choice -like Vahlen describing Thin Men as having 'reptilian features', and then Tygan describing Vipers as 'wholly reptilian'- but it also goes into the deeper layers of fundamental worldbuilding decisions. Snakemen, though classic X-COM didn't tell us anything about their society, were operating from a radically different foundation that would be tremendously unlikely to share many features found in many human civilizations. Marriage seems very unlikely to be an institution in Snakeman society given they likely don't need two parents to produce a kid, as one of the most obvious elements. Vipers are instead mono-female as something of a callback to Snakemen, but with an underlying explanation that places the mono-female quality as a temporary product of brutal Ethereal oppression, where the undertone is that Viper society divorced from Ethereal influence would look more or less exactly like human society.

By a similar token, Viper combat capabilities are pretty directly reflexive of stock pop culture memes that go back... well, literally hundreds or thousands of year. Vipers don't do anything alien, don't have any capabilities that fly in the face of our stock expectation of what a big reptile might do. They spit poison, like a spitting cobra. They Bind your soldiers, like an anaconda suffocating its prey by wrapping it in its body. They have Tongue Pull, because people have been mentally shoving together reptiles and amphibians for centuries so sure why not give the snake-lady a frog tongue.

Literally their only alien quality is that they're supposed to be the true form of Thin Men back in the prior game, except oh wait that isn't an alien quality, that's just Ethereal 'genetic manipulation'. It's not that Vipers are natural shapeshifters, where Thin Men are the closest approximation to humans they can manage using their natural shapeshifting. Narratively, any alien could've potentially served, and all that would've been different would've been the exact form of creepy off-ness that resulted.

Which is frustrating because, as far as an intersection of gameplay and narrative elements goes, it would've actually been pretty brilliant to have Vipers fill the role Faceless currently fill of 'it's a civilian, up until you approach it and it throws off its disguise', leveraging the Thin Man thing, making Vipers feel way more alien, and substantially reducing the whole 'Faceless are an amazing concept that XCOM 2 pretty much completely wastes'. (It would probably have some strangeness, admittedly, but still)

Vipers are probably the biggest offenders here, but this recurs a fair amount. I actually kind of like the Muton tribal culture thing, but I can't help but be aware it's also an example of the Firaxis games making their aliens... less alien, where Mutons are Random Tribal People Given Guns, and it's largely immaterial that the tribal people in question were plucked from a far-off world and technically aren't human. Indeed, it's perfectly valid to interpret Firaxis Mutons as literally being humans the Ethereals picked up a few centuries ago, where they only look as inhuman as they do because the Ethereals have been modifying them into a dedicated soldier caste for centuries. It's clearly not the intended explanation, of course, but it's... a lot more functional a theory than it should have any right to be.

Even the Ethereals suffer a bit from this. Classic Ethereals were a species that had collectively all gotten so obsessed with their psychic powers that they disdained physical activity to the point of suffering severe atrophy, only able to survive on fairly literal willpower. You can argue it's a metaphor for real people doing stuff like spending too much time in front of their computers and not enough time exercising, ending up out of shape as a result, but it's taken far enough it's made into a fairly inhuman choice. Firaxis Ethereals are... four-armed humans with magic powers, who as of XCOM 2 are suffering severe atrophy due to some genetic condition they don't know how to cure. That's about as alien as a wizard with cancer.

Surprisingly, War of the Chosen actually shows signs of reeling back this trend, even though the Chosen in the title are literally humans, but I'll get into that more in a later enemy post.

Overall, I'm not a fan of Vipers in XCOM 2, for both their unclear gameplay design and their baffling set of narrative elements. If it weren't for Chimera Squad coming along and giving us Torque, I might even be tempted to say I'd rather they'd never been a thing at all. As-is, I still have concerns regarding how XCOM 3 might handle them.


Next time, we jump a bit to the side to cover one of the more unique enemies of the game: ADVENT Turrets.

See you then.


  1. I assumed Tygan was some form of neurosurgeon, given his work with ADVENT before defecting. Then his capacity to do ALL THE SCIENCE is just a Hollywoodism. You can pretend that Shen helps him with some of the more engineering-adjacent projects (implied in some of the autopsies, IIRC), or maybe some of the scientists you rescue just happen to have the relevant expertise to crack whatever science project, and Tygan is just reporting the results. I assume the XCOM devs gave zero thought to this, and hoped the common "polimath genius scientist" trope would carry the willing suspension of disbelief.

    I liked your overview of possible explanations for only fighting female Vipers in the game that involved something else than population control from the ethereals. Seemed very thorough, and I learnt a few things!

    Now I am curious what you think of Torque, and in what way she redeems the species.

    1. Tygan's specialty or lack thereof is a sufficiently complicated topic I intend to cover it in detail in a different post, but the really short version is that XCOM 2 is a huge improvement on this topic (In the prior game, Vahlen was 100% always an omnidisciplinarian expert, where in XCOM 2 Tygan has some hints of being focused to some extent and Vahlen is made retroactively focused on biological sciences), but Tygan still has a lot of moments where he knows things well outside any possible knowledge base. (See: pretty much all his dialogue regarding Codices)

      Also, yes, Shen is consistently indicated to be involved when it comes to mechanical enemies. She doesn't actually show up in the Autopsy cinemas, which is a shame, but the game is consistent on this point, and more subtle is that when you first sight an enemy Shen will generally chime in if the unit is mechanical -and usually Tygan WON'T speak up in such cases. It's one of the lower-key elements of XCOM 2 I genuinely appreciate.

      I'm going to do at least class/character posts for Chimera Squad once I'm done with the XCOM 2 posts, but for the moment I'll note I just generally tend to like 'evil'/mean characters like Torque if a story engages with them as people (Instead of villains to be righteously punched in the face who could not possibly have reasons for their actions) and so it's less 'Torque redeems the species' and more 'if a random divinity asked me to choose whether to make our timeline the real one, or a different timeline with no Vipers and no Torque in these games, I'd agonize over whether my fondness for Torque outweighs my dislike of Vipers in XCOM 2'.

      ... well, that and Torque's gameplay is one of my favorites in Chimera Squad, while being extremely faithful to Viper mechanics. Turns out Vipers make for much more interesting player units than enemies!


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