XCOM 2 Alien Analysis: Decaying Turret

HP: 4/4/5/6
Armor: 1/2/3/3
Defense: 0
Dodge: 0
Aim: 50
Mobility:  0
Damage: 3-4 (+1)
Shred: 0
Crit Chance: 0
Will: 50
Tech: 30/30/35/35

Mechanical Chassis
This unit is a robot, rendering it immune to Poison, Fire, and Chryssalid Poison as well as most psionic or mental effects (Including that it will never Panic or be rendered Unconscious), but susceptible to anti-robot effects and impossible to heal with Medikits.

Like Derelict Mecs, this makes them really easy to kill with lady Shen. Her Combat Protocol and Capacitor Discharge both do 10~ damage to robots, so even on Legendary that's an automatic one-hit-kill. (You should optimally have Shen target unharmed Derelict Mecs and Decaying Turrets, incidentally, to maximize squad effectiveness) Also like Derelict Mecs, this slightly encourages bringing regular Specialists, while the other implications are unlikely to matter unless you deliberately put off hitting Lost Towers.

Hardened
Does not use Cover, but is never considered to be in the open.

Like Derelict Mecs, this is an important part of making SPARK-001 look good. It's a bit less effective, though, as Decaying Turrets all spawn on the highest available ground, whereas Derelict Mecs tend to end up in low ground after spawning; SPARK-001 is a lot more prone to missing Decaying Turrets as a result.

Also note that Decaying Turrets are all placed on indestructible terrain, and so you can't actually instant-kill them with explosives the way you can most ADVENT Turrets. As a result, they actually tend to pose more of a challenge than ADVENT Turrets in spite of having an identical statline to Basic ADVENT Turrets!

Bullet Storm
Firing does not end the unit's turn, and it has unlimited ammo.

Like regular ADVENT Turrets, Decaying Turrets have AI shackles preventing them from using this to fullest effect. Unlike ADVENT Turrets, I've never actually seen a Decaying Turret shoot twice or shoot and then go into Overwatch; as far as I'm aware, their ability to spend both action points only matters because Shen can steal them with Haywire Protocol.

Incidentally, it's worth pointing out that Haywire Protocol actually functions like Domination in the sense that if the controller leaves the map or dies the Hacked unit leaves your control. In normal play this is so completely irrelevant 99% of the time that I honestly forget it's a thing at all. (Especially since the game doesn't have a visual connection effect between controller and controlled the way Mind Control gets) In Lost Towers, it actually matters, since the elevator-evac mechanic can lead to you having Shen Haywire Protocol a unit, then on a following turn evac while the controlled unit is still around. Make sure you have any such Hacked unit act before you have Shen evac!

Speaking of Lost Towers...

Decaying Turrets show up exclusively on the second map of Lost Towers, hence part of why I saved covering the second map for this post.

By extension, I'll be talking about the second map of Lost Towers instead of making general observations much for the same reasons as I covered the first map in the Derelict Mec post.

Like the first map, you start out under no pressure, in spite of the first map ending with an infinite tide of Derelict Mecs spawning in to kill your squad. If you've got injuries from the defense of the previous map's elevator escape, now's a good time to have Shen heal people up, probably the best time in fact.

Once you start advancing, there's actually only two Decaying Turrets on the entire map to start, both of which will immediately come into view if you have someone spend one full action point on advancing. Feel free to have Shen Combat Protocol one out of existence while the rest of the squad tries to shoot the other. If you've got a Grenadier with Suppression, it can be good to have them Suppress the other Decaying Turret if the rest of the squad fails to kill the second Decaying Turret: even with high ground advantage, a Decaying Turret under Suppression can't hit a soldier in any form of Cover, bar Aiming Angles kicking in... which the Cover in the area is designed to prevent Aiming Angles from kicking in, so that shouldn't be a concern.

Caveat: if you're playing on Legendary, there's actually four Decaying Turrets to start, with the additional two off to the sides of the original two. As you're still under no time pressure at this step, it's a bit pointless: you can always just have someone spot for Shen using Combat Protocol, mash end turn until Combat Protocol is ready, and repeat until they're all gone, with no danger at any step. I'm not sure why the devs made Legendary difficulty do this.

In any event, once you've got these Decaying Turrets dealt with, you're still under no pressure. Feel free to reload and have everyone Dash to positions in the center of the map: this has zero possibility of going wrong. The game will direct you to have Shen activate the SPARK, advancing to a specific tile in the center of the central building: don't do this until you've got your entire team in position, with action points to spare, as it triggers Decaying Turrets to start spawning in and after a delay of a turn causes every part of the map outside the SPARK's little building to fill with poison gas.

(A nice touch: the windows for this little building are unique and appear to be some kind of forcefield, as opposed to the glass and/or laser fencing seen throughout XCOM 2 otherwise. This makes it believable your team can be safe from a poison gas by staying inside the room while still getting to exchange fire with Decaying Turrets through the windows. It's pretty easy to imagine a coherent physical model for these forcefields keeping out poison gas while letting bullets and soldiers pass through)

Note that on Legendary in particular, the initial wave of reinforcements includes two Derelict Mecs. It's a good idea to set up Overwatch on the forward area to try to do some damage to these Derelict Mecs.

So how does a Decaying Turret 'spawn in', given it can't move? Why, they're pop-up turrets, with a series of specific tiles bringing them up by elevator. You can see one of these panels in the above screenshot through the poison gas; it's the black-and-silver square on the lower-left. They all look like that, so you can identify all possible Decaying Turret spawn points and indeed identify the maximum number of spawns in the map. Note that this pop-up behavior is not considered to be movement, and so you can't catch spawning-in Decaying Turrets with Overwatch. Alas.

Anyway, activating the SPARK grants it to you as a fully functional soldier, but the turn you activate it leaves it (And Shen!) with 0 action points, so it can't help just yet. The following turn, you will be directed to have the SPARK go activate an atmosphere thing to drain out all the poison gas, which is over at the far end of the map. You might expect this to be a Hack point to show off the SPARK's remote Hacking ability, but no, the SPARK has to physically enter the tile to activate it. On the plus side, activating it costs no action points, so you can move to it, activate it, and still have SPARK-001 contribute against a Decaying Turret.

Speaking of, activating SPARK-001 causes 2-3 Decaying Turrets to pop in per turn until all the slots are filled in. One of these sets is actually a pair spawning close together behind the building: this is another good opportunity to have Shen use Capacitor Discharge.

Now, you might think you're not really under time pressure at this step. Only so many Decaying Turrets, after all, right? Just kill them all and leisurely make your way to the next...

... map. Oh.

Yeah, once there's no Decaying Turret pop-up slots left to fill, Derelict Mecs start dropping in instead. Like the Derelict Mec spawns on the first map, as far as I'm aware these go on infinitely. So no, you can't just kill everything and move on at leisure, you've got to run.

Indeed, once you've had SPARK-001 clear the poison gas, it's time for another round of fleeing up an elevator, complicated by the fact that everybody except SPARK-001 is, of course, toward the middle of the map at this step. And you can't just have them Dash for the elevators, because the constant stream of enemies will kill people if you try. So this is a running, fighting retreat.

On the plus side, there's two elevator slots on the second map, so you can get the entire squad out in 3 turns. (If you haven't stalled long enough to get the second squad size expansion upgrade, which the game clearly doesn't intend for you to do) That makes it a little less hectic than on the first map. You also don't necessarily need to kill all the Decaying Turrets: they can't pursue your squad to the elevators, and indeed the elevators are boxed off in a manner that means even nearby Decaying Turrets can't actually fire on someone hiding in the box. Once you're down to 1-2 soldiers waiting to flee, they can hide back there, at which point it's basically only Derelict Mecs primed to self-destruct already that might be an issue.

Do note that if SPARK-001 goes down you get an immediate game over. As such, even though it's probably your toughest squad member, you probably shouldn't have it be one of the last to go up the elevators, especially since you can't fix it up mid-mission, unlike your organic soldiers. It probably won't take a hit, given it has 15 innate defense and Lost Towers' enemies have poor innate Aim, but no reason to risk the enemy getting lucky.

Also, something mildly exploitable to note is that the poison gas filling the room is, in fact, regular Poison gas, which is to say your soldiers can be immune to it via equipping Medikits, having the Fortress ability, or equipping Hazmat Vests. It's only mildly exploitable; first of all, the elevators don't activate until you've cleared the poison gas, so you have to clear it out no matter what. Second of all, the value of doing Lost Towers early is getting an early SPARK, and fully exploiting Medikit-provided-immunity to the gas requires putting off Lost Towers until you've got Predator Armor, so you can pass out Medikits without sacrificing grenades. It's still something to keep in mind, as you can potentially get Fortress very early on a Templar, and you can also pass out a Medikit to a key team member if there's someone you want able to range out. (eg a Templar, a Ranger you want able to melee effectively)

That's really the whole of the second map, and we'll be covering the third map next post, for similar reasons to this post handling the second map.

Aesthetically, Decaying Turrets are a fine execution of a straightforward concept: they're ADVENT Turrets that have rusted for years with little or no maintenance.

I don't enjoy this as much as Derelict Mecs, but it's solid enough. Even if it's a bit strange that their statline isn't any worse than a Basic ADVENT Turret...

Narratively, Decaying Turrets are interesting primarily for how they tie into the possibility of the robo-retcon I covered in the Derelict Mec post: that it's possible Lost Towers is where ADVENT Turrets were first designed and built, in-universe.

To be honest, I suspect Decaying Turrets are a thing purely because base XCOM 2 has so few robots to work with in the first place, with any resulting narrative coherency being happenstance.

But I do still have to wonder.

Gameplay-wise, I'm a little surprised War of the Chosen didn't incorporate the pop-up behavior on ADVENT Turrets, not even in Chosen Strongholds. Not complaining or anything, and War of the Chosen was clearly rushed so it's not that surprising, but still, it is a little surprising. I don't think a mod has tried to implement it, either, which is slightly more surprising.

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The first map had its own unique music, and so does the second one. More precisely, it actually uses the first map's tune when you're fighting the initial Decaying Turrets, but once you've activated the SPARK it switches to this new tune.

Like the first map, it's a really nice tune I'm sad you have little reason to actually hear. It's probably my favorite of the Lost Towers-specific tunes, in fact.

Also like the first tune, it only has one version, instead of a version for your turn and a version outside your turn.

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Next time, we'll wrap up Shen's Last Gift with the Prototype Sectopod.

See you then.