Doom Roguelike Equipment Analysis: Rocket Launchers

Before talking about Rocket Launchers, I need to cover several mechanics that are heavily pertinent to them.

First is Fire damage, as Rocket Launchers all use it: this is the 'boring' energy damage type, with no special tacked-on mechanics, making it the energy damage equivalent to Bullet damage...

... except there are three mechanics that make this less true than it sounds.

First is terrain destruction. Walls by default function rather like enemies do, in that they have a certain amount of HP and Protection and are destroyed when their HP runs out, but with several key differences: a wall's Protection can reduce damage to 0 (And often will: walls normally have 10 Protection!) unlike Protection on units and Doomguy. A wall also ignores damage entirely if it's not the right type: only Fire, Plasma, and Acid attacks can actually reduce wall HP. The Trigun hitting for up to 18 Bullet damage? Does nothing to walls. Also, Plasma ignoring half the Protection of the victim? Doesn't apply against walls. So you must have a Fire, Plasma, or Acid attack that can do over 10 damage if you want to knock down walls.

When those conditions are met, walls normally shred quite quickly! They only have 20 HP, typically, which is more than really early enemies like Imps, but the serious threats uniformly have more.

All this comes with the caveat that not all terrain is 'hard' terrain. Some terrain is 'soft': doors, a certain type of crate terrain that often drops loot when smashed, and...

... all walls if you get the rare Hell Freezes Over event. These can be destroyed by any damage type. Careful with corner-shooting your Shotgun in such cases!

Then there's the consideration of item and corpse destruction. Items and corpses on the ground don't normally interact with attacks: shots pass right over them with no effect. Splash damage (Both the Shotgun-style strike zone and the Rocket Launcher-style explosion) is a caveat that can destroy such... if the splash is Fire, Plasma, or Acid damage. Shotgun splash never destroys items, period, and normally you won't see it shred corpses, but that's because most Shotguns do Shrapnel damage: a Plasma Shotgun or any Shotgun you've Assembled into a Plasmatic Shrapnel version will shred corpses in its entire strike zone, because they do Plasma damage and that counts.

In the case of corpses, standard corpses have 1 HP and inherit the Protection value of their base enemy, and like walls they're allowed to reduce incoming damage to 0. Archviles leave a corpse, but their corpse is a 'bloody corpse' that doesn't really count as a corpse for most purposes and doesn't inherit their Protection stat. In practice most bodies will be shredded by most attacks that have the correct damage type, but for example the Mega Buster's Acid and Fire Modes can roll low enough on damage to fail to overcome Protection.

Items have a simple binary: was their tile hit for 10 or more damage by an explosion? (I'm unsure if damage type matters here per se: all explosions are Fire, Plasma, or Acid damage in the versions of the game that I've played) If yes, the item is destroyed. (Unless it's a Unique) If no, it survives. Items don't have invisible HP meters or anything like that.

Third is a mechanic it's easy to be unaware of, inherited from classic Doom. (Where it was also easy to be unaware of it) Gibbing!

When an attack kills an enemy, it's possible for that enemy to not actually leave a body. Bullet, Shrapnel, Melee, and the rare Piercing damage type can only trigger this if the killing hit rolled for at least 400% of the target's maximum HP. eg if you hit an Imp (12 HP) with some outrageously powerful Shotgun, it would need to deliver 48 damage for the Imp to not leave a body. Note that the game doesn't resolve simultaneous actions simultaneously: even though a point-blank Super Shotgun can theoretically deliver 60 damage in one pull of the trigger, it delivers its damage as two shots the game resolves separately, so an unmodded Super Shotgun can't gib an Imp. Also note that this is not a 'negative HP' concept like some games use: an Imp at 2 HP still needs to be hit for 48 damage to be gibbed, not the 38 damage you might expect from it already missing 10 HP. This is part of why gibbing is easy to be unaware of: it's very demanding to actually pull off!

Plasma and Acid damage are better at gibbing. They only need to do 200% of max HP in damage to gib. (So 24 damage to gib an Imp) The player has almost no access to Acid damage and Plasma damage is mostly accessed in the form of weapons spitting out weak shots rapidly, so this doesn't come up much.

Fire damage is where it's at: Fire damage only needs to do 150% of the target's max HP in damage to gib the victim. As most Fire damage the player has access to is in the form of single big hits, it's pretty normal to gib the weak enemies (Assuming you bother to fire a Rocket Launcher at a Former Human or similar), and even some of the middling durability enemies aren't too surprising to gib on occasion.

Though as previously covered, the secret BFG Plasma damage type is even better at gibbing, doing so at 100%, so Fire damage isn't truly king of gibbing. But Fire damage is way more accessible than BFG Plasma damage, so for large parts of a lot of runs Fire damage will be functionally king anyway.

Do note that when an enemy is gibbed, they not only don't leave a corpse but also don't leave behind any gear they're supposed to drop, such as ammo. Say you're wanting more Shotgun ammo: in that case, you shouldn't necessarily aim your most deadly weaponry at Former Sergeants, because if they're gibbed you're not getting that ammo!

Last to cover in regard to Rocket Launchers in general is explosion damage, as all Rocket Launchers use it and they're the player's main source of explosions. Explosion damage is... funky.

For tight explosions (Ones with a radius of 1), explosions are straightforward to understand: they unavoidably hit everything in the tiles caught in the explosion radius, doing full damage. The only wrinkle you might be caught off guard by is one shared with Shotgun damage: that damage is rolled separately for each caught target, allowing for unintuitive outcomes like 'the Former Captain I hit dead-on survived, while the Former Captain standing next to him died'.

Radius itself, I should note, is 'how many tiles out from the center does this hit'. Radius 1 is 'hits directly adjacent tiles', for example. I don't really understand the rules for how it expands past radius 1, as larger explosions produce diamonds, not ever-larger squares. It feels inconsistent to me.

Regardless, once you are 2 or more tiles away from the impact point, damage drop-off finally occurs, but it's... not at all like Shotgun damage drop-off. Instead, the game does a funky math trick: damage starts from 1 divided by 1 (Which produces 1), but that second number goes up by 1 every two tiles out. So at three tiles you divide 1 by 2 (Producing 0.5), and that's used to modify your damage: thus, at three tiles out, damage suddenly drops massively (Halved), but while damage continues to be lost as you move further away from the impact point, the loss is much slower past that first drop.

eg at 4 tiles out you divide 1 by 3 (Producing 0.33), and so your damage is now 33% of base: that's lower, yes, but it's about 66% of what you do at 2-3 tiles out, not 50%. At 6 tiles out you're doing 25% of base, which is about 76% of what you were doing at 4-5 tiles out. The currently largest strike zone in the game is radius 16, and you're still doing 12.5% of base damage at the edges!

I'm personally not a fan of this system, as it makes having a blast radius at all pretty high-impact, but means having a higher radius is very low in value except when specifically wanting to clean corpses rapidly. It also has the effect of making it so a high radius on something reliable about destroying items in the center generally has pretty good odds of wiping out items at the edges even on very large blast radii, which is frustrating and unintuitive, making a high radius not particularly helpful at killing enemies but still heavily increasing the risk of blowing up valuables.

I don't get why explosion damage isn't more like Shotgun damage in terms of the drop-off mechanics.

I should also point out explicitly that when an explosion causes knockback, the knockback is defined relative to the explosion's center, unlike a Shotgun knocking targets away from Doomguy. In the case of a direct hit, knockback is applied consistent with the projectile's trajectory: you fire a rocket straight east and it hits an enemy, that enemy is launched directly to the east. This comes with the funky qualifier that a projectile hitting a wall and then exploding sources the knockback from the wall the projectile hit, not the tile the explosion gets centered on. So for one thing firing on an enemy whose back is to the wall can produce unexpected results, feeling just plain random if you aren't familiar with these details.

Anyway, that's a bunch of important context covered; on to specifics. Uh... all four of them. This is the smallest weapon category, for whatever reason.

(Basic) Rocket Launcher
Damage: 6d6

Accuracy: +4

Fire Duration: 1 second

Reload Duration: 1.5 seconds

Clip: 1

Alternate Reload: None.

Alternate Fire: Rocket Jump. Fires a rocket that explodes after traveling 1 tile. This rocket inflicts half normal damage to Doomguy in specific, but calculates knockback using the full damage roll and has the most generous knockback rate in the game; 1 tile of knockback for every 2 points of damage. (Next-best is 1 tile per 7 points of damage, for comparison)

Blast radius: 4

Minimum floor: 7

Your basic, generic Rocket Launcher. 

Something easy to be caught off guard by is that the Rocket Jump is actually unique to it, so if you're a big fan of the Rocket Jump you're going to want to carry around a basic Rocket Launcher, not just ditching it the second you get a Missile Launcher. The Rocket Jump is itself a way to cross Acid/Lava rivers at a low HP price (A max damage roll will do 18, which hurts, but Running across three tiles of Lava will do the same damage by default. And in actuality your bodily Protection and resistance is often higher than your foot Protection/resistance: a Red Armor would roughly halve that damage), to disengage from melee groups at a low HP price, or otherwise abruptly move a great distance: just rolling toward the middle of its damage range can be nine tiles traveled in 1 second!

The Rocket Launcher itself is in an odd place. In 'standard play' (By which I mean on regular floors), it's a problematic weapon to try to use to solve your problems: it hits quite hard, but most serious threats will survive at least one rocket 100% consistently, and against groups it will scatter them every which way, creating problems for following up. You'll also need to reload after every shot (Which is a bit slow if you're not using Shottyman to bypass the base reload time), it missing can cause unexpected outcomes (eg hitting a wall behind an enemy and launching them closer to you), you're often risking destroying items (Often without being able to determine for sure that you wouldn't mind if they got blown up), you're often risking destroying walls and so potentially suddenly bringing in more enemies with little warning, and its generous blast radius means there's a pretty narrow slice of terrain where you can see your target but won't be hit by the explosion yourself. This is further exacerbated by one of the swarmiest enemies of the game being a lightning-fast melee-only enemy with severe Fire resistance, making a Rocket Launcher really bad at dealing with what seems like it ought to be a great target.

This is a big problem with how much the Rocket Launcher overlaps with Shotguns, with many of the differences being to a Shotgun's favor. Shotguns never miss, have much more predictable and favorable knockback mechanics, can't destroy valuable items, (mostly) can't unexpectedly destroy walls, can't hurt Doomguy by pulling the trigger (Except through carelessness around Barrels, but that applies to everything except melee attacks), have a better ammo situation, all while still being a way to apply damage to large groups of enemies at once. A Rocket Launcher isn't burdened by the Shrapnel damage type, can clear corpses, and has better damage modification at long range to centermost victims (But reminder that a basic Shotgun does 44% damage right at edge of sight, which is barely worse of a modifier than a Rocket launcher suffers against anything hit but outside the central 9 tiles), but overall it's a bad trade, even before considering two classes have a Mastery for specifically improving Shotguns and only the Technician has a Mastery that even ostensibly specializes in rocket usage. (It's also ignoring that if you don't perfectly understand corner-shooting's rules, a Rocket Launcher can horribly backfire where a Shotgun can at worst oops destroy your corner. And most of them can't even do that normally)

But, in a standard run, the Rocket Launcher is a very notable tool for getting through several Special Levels. Special Levels having fixed design means that in several of them you can fire a Rocket Launcher in some direction with full confidence that this can't backfire in any capacity, and in a standard run you get a very early Rocket Launcher the game expects you to use to get past key early challenges. (Such as the Arena Master) As such, a Rocket Launcher is an important part of your arsenal just for that reason.

Furthermore, a Rocket Launcher is your default means of punching through walls. One Special Level pair is premised under this fact (The Wall/Containment Area, where everything of use is locked away behind a wall you're expected to destroy), and for regular floors you'll occasionally get a floor generate such that you must either go through a river of Acid or Lava or knock down walls to avoid needing to do that wading. Spending a rocket or three to avoid having to go through the deadly river can be a good trade.

But I mentioned a bad ammo situation earlier, and it's time to get to that.

Rocket Ammo

10 rockets at most per tile or inventory slot. When generated on the floor, spawns as a stack of 6/3/4/4/6 Rockets. (Difficulty-dependent)

Minimum floor: 5

Yes, Hurt Me Plenty and Ultraviolence both end up with the same ammo value in spite of the differing modifiers. I'm honestly surprised the game doesn't round up the Ultraviolence amount.

In any event, Rockets are by far the worst-off ammo type in terms of raw numbers, with a tenth the space efficiency of 10mm ammo and a fifth the space efficiency of Shotgun Shells and Power Cells. This is misleading in practice since 10mm ammo and Power Cells are often spent multiple units at a time, whereas Rockets are never spent more than 1 per pull of the trigger, but the Shotgun Shell comparison works more directly: 10 pulls of the trigger on your basic Rocket Launcher vs 50 pulls of the trigger on your basic Shotgun! Rockets also don't spawn very much in general: only two regular enemies drop Rockets on death, and each only drops 3 Rockets apiece, and of course Rockets generated on the floor don't generate in large stacks. In 0.9.9.7, ammo rooms contributed to the problem, as only floors 9, 10, and 11 even could generate ammo rooms with Rockets in them, and no floor was guaranteed to have an ammo room be a Rocket room.

Also, there's that item destruction issue. With most weapons, breaking them out to kill enemy types that drop the matching ammo (eg Shotguns for Former Sergeants, Plasma Rifles for Former Commandos) is a sensible strategy for smoothing out your overall ammo management. With a Rocket Launcher, you're going to end up smashing the ammo drops! Notably, the order in which the game processes explosion damage seems... incoherent. You'd expect that firing a Rocket into a Revenant and killing it that way would assure the survival of the ammo, and that is sometimes what happens, but sometimes an explosion will destroy drops from enemies who were killed by that explosion. I assume the game's internal logic for processing explosion damage is working through the tiles one at a time and knockback is allowing situations where an enemy is killed in one tile, but instantly shoved into another tile that gets processed later in the explosion routine and so the explosion 'double-dips' and destroys the corpse and its loot. Whatever the reason for it, even firing a rocket into a single Revenant and stopping as soon as it's dead may still blow up your Rocket loot.

These ammo issues are a big factor in relegating Rocket weapons to a secondary role.

Of course, Rockets have their own quick-reload ammo item:

Rocket Box

25 rockets per box.

Minimum floor: 7

The Shell Box of Rockets, the Rocket Box packs in 25 Rockets into one inventory slot and can be equipped in your Prepared slot to give you an 80% reduction in reload times. (In 0.9.9.7, it was slightly less good, only cramming 20 rockets into one inventory slot)

It saves exactly 30 seconds of reloading over its lifetime with a basic Rocket Launcher.

With a Missile Launcher or Napalm Launcher, it saves 24 seconds of reloading over its lifetime.

With the Revenant's Launcher, it saves 28 seconds of reloading over its lifetime.

Like Shell Boxes, Rocket Boxes are a huge aid to combat performance. Unlike Shell Boxes, Rocket Launchers are actually useful for non-combat purposes like knocking down walls and Rocket Jumping, and for those purposes using a Rocket Box is a bit wasteful. If you have no intention of using a Rocket Launcher for combat, it's arguably not worth picking up Rocket Boxes at all unless you have no regular Rocket ammo: you only really need the one inventory slot for such, and a Rocket Box adds inventory clunkiness from needing to be put into the Prepared slot to reload from it.

Missile Launcher

Damage: 6d6

Accuracy: +10

Fire Duration: 0.8 seconds

Reload Duration: 1.2 seconds (Reloads entire clip)

Clip: 4

Alternate Reload: Full Reload, taking 0.2 seconds longer than it would take to manually reload all involved shots.

Alternate Fire: None.

Blast radius: 3

Minimum floor: 10

Just like with Combat and Assault Shotguns, Full Reload doesn't make sense to do by default, but can make sense when benefitting from a buff since those have their timers action-based rather than seconds-based. Most obviously so with Invulnerable.

By default, the Missile Launcher is a big improvement in combat viability over a Rocket Launcher: same damage, but way more Accurate (It will always be capped on hit chance on anything you can actually see), taking less time to fire, taking less time to reload, and getting to fire four times in a row before a reload is even necessary. The only losses are that it lacks Rocket Jump and that its radius is tighter -but I'd argue its tighter radius is really another advantage, making it less prone to costing you by smashing items and knocking down walls unexpectedly. If you tend to forget Rocket Jump even exists... well, then it really is basically pure improvement.

Note that in a standard run there's multiple Special Levels that are guaranteed to have a Missile Launcher (Containment Area/The Wall and City of Skulls/Abyssal Plains), so you can very reliably make the swap from a basic Rocket Launcher. So for one thing if you're thinking of modding your Rocket Launcher, keep in mind you may well be ditching it in short order.

Do note that there are multiple Assemblies for a basic Rocket Launcher and 0 Assemblies that 'target' the family of Rocket-using weapons. If you're wanting to make one of those Assemblies, you shouldn't mindlessly ditch your Rocket Launcher as soon as you have a Missile Launcher.

Aside the Assembly wrinkle, the Missile Launcher really is mostly a straightforward and great improvement.

Napalm Launcher

Damage: 7d7

Accuracy: +10

Fire Duration: 0.8 seconds

Reload Duration: 1.2 seconds

Clip: 1

Alternate Reload: None.

Alternate Fire: None.

Blast radius: 2

Minimum floor: 10

Special: Tiles in blast radius will frequently be replaced with Lava tiles.

The Napalm Launcher is a quirky gimmick weapon whose 'collateral damage' issues are in some ways worse than ever (In spite of its absurd Accuracy and tighter blast radius), but which has much higher damage potential than you might assume and is especially useful anytime you're worried about corpses getting back up, since fluids eat corpses 100% reliably.

0.9.9.8 is a bit of a mixed bag for the Napalm Launcher in spite of it not receiving any direct changes. In 0.9.9.7, Archviles feared hostile fluids but didn't take damage from them, making the Napalm Launcher worse against them than it ought to have been, while 0.9.9.8 corrected this so now trapping an Archvile on Lava is a death sentence to it... but 0.9.9.8 also made all 'Nightmare' enemies completely immune to hostile fluids. If you're playing on lower difficulties and don't touch Angel of 100 or Archangel of 666, this doesn't really matter to you (Nightmare enemies can show up in Limbo in specific on even low difficulties, but that's it), but on higher difficulties and/or late in an Angel of 100/Archangel of 666 run, this is a pretty big hit to its utility!

If you don't expect to Assemble Cerberus Boots (And haven't lucked into alternate fluid immunity), the Napalm Launcher is pretty powerful but something you need to use judiciously and with a good awareness of your environment if you don't want to end up wading through Lava repeatedly. If you do have fluid immunity, it becomes a lot better, albeit still hampered by the potential to destroy items: a Nanomachic Napalm Launcher coupled with fluid immunity makes for a very funny run where you just cover the map in Lava and don't care about the collateral damage. (I did this once. It was fun) Do keep in mind that plenty of enemies are immune to hostile fluids, especially late in an Angel of 100/Archangel of 666 run: even before 0.9.9.8 added Nightmare enemies to the list, it was already the case that all the boss enemies that show up starting from floor 80~ were immune, as well as Cacodemons, Lost Souls, Pain Elementals, Elite Former Commandos, and in 0.9.9.7 Archviles and Nightmare Archviles were immune. So in such runs, just covering a map in Lava gets increasingly unreliable: you'll have to actually shoot enemies.

Personally, I usually skip Napalm Launchers I find: I like the idea of them, but the reality is easy to screw yourself with, and doesn't actually have that much unique utility to it. If Missile Launchers weren't guaranteed in standard runs, I might be tempted by the absurd Accuracy, but they are guaranteed, so I can get the great Accuracy without risking having to wade through Lava afterward. And a Missile Launcher has the same fire speed, reload speed, and a much larger clip size... the Napalm Launcher does hit harder per shot, but not by much.

Revenant's Launcher

Damage: 7d6

Accuracy: +6

Fire Duration: 1 second

Reload Duration: 1.4 seconds

Clip: 1

Alternate Reload: None.

Alternate Fire: None.

Blast radius: 3

Minimum floor: 12

Special: Automatically detonates at the targeted tile if nothing interrupts its flight path, instead of only stopping on impact.

Scavenge result: Sniper Mod Pack

Note that as of 0.9.9.8, Technicians can fully mod a Revenant's Launcher as if it wasn't a Unique at all. This is, uh... narrow. Nanomanufacture Ammo is literally the only Assembly that can be applied to it. That can be incredible if you happen to have a Technician find both the Revenant's Launcher and a Nano Mod Pack in the same run, but is pretty unlikely to happen. More likely is just super-modding it: reminder that Sniper packs are useless to it and Accuracy packs technically benefit it but its mechanics mean this isn't so in real terms. So you can only put Power (Adds a d7 per use), Bulk (Reduces reload time by 25% per use), Technical (Reduces firing time in an opaque but mild way per use), and Firestorm on it. (Increases blast radius by 2 tiles per use) It's weird to me that this got full moddability and not any of the Unique Weapons that would have a new world of potential added to them...

... though I suspect that's precisely why it got full moddability: less effort to implement, if Assemblies have to be manually implemented per valid target. Which I suspect they do.

Regardless, the Revenant's Launcher is the ultimate in rocket launcher behavior, and even for non-Technicians is difficult to push off its throne with Mod Packs. It can take some getting used to as its mechanics are not properly explicated and the animations do less good a job of communicating what is happening than is ideal: even if you figure out that it being named 'Revenant's Launcher' is as in 'it uses Revenant rocket mechanics', the game is poor at communicating how those work! And in a standard run, you'll see Archvile ranged attack mechanics first, which are often functionally the same and so can leave one with an inaccurate impression of how Revenant shots work.

Said mechanics are that the Revenant's Launcher has standard rocket behavior with one exception: if the shot doesn't connect with anything before it reaches the tile you clicked on, it detonates upon reaching exactly that tile. So if you fire on an enemy standing behind other enemies, you'll probably have the shot detonate on a target you didn't click on, but if nothing is in the way, you'll definitely hit your clicked target...

... except that this is another case where it's really easy to get fouled up by the fact that Dodge does in fact apply to Doomguy targeting enemies, not just enemies targeting Doomguy. If you roughly understand the 'detonates on target' behavior (Whether your intuition is aligned with the reality or you're incorrectly guessing more Archvile-type behavior), the natural thing is of course to prefer to click directly on enemies... which will give Dodges a chance to trigger. Causing you to target the tile they were in on your previous turn. With terrain about, this can result in you targeting with an angle to have the shot get caught on a wall (Which will be mystifying as to what happened if you don't know about this Dodge symmetry issue), potentially a wall really close to you!

Unfortunately, like Gun Kata's jank with Dodge interaction, this isn't fully avoidable. You can prefer to target right in front of your desired target, and that'll often be fine if only one enemy is about, but when groups of enemies are hanging together? You might not be able to avoid clicking directly on any enemies without having to accept consequences that are also undesirable. (Smashing items, hitting fewer enemies, applying knockback in directions you don't want it applied...)

Outside this frustrating bit of jank, the Revenant's Launcher largely escapes the collateral damage problem other Rocket-using weapons are haunted by. It can still destroy items and all, but the 'detonate at target' behavior means you can fully reliably aim it at locations where you know this risk doesn't exist. It's also very effective in conjunction with Intuition 2, since you can fire at the edge of your vision to 100% reliably hit whatever enemy you're detecting via Intuition for full damage, though obviously that has the risk of item destruction if you're not firing into known terrain.

Do keep in mind that if you like to fire into the darkness to hit enemies at extreme ranges (via a Tracking Map telling you that they're right up against a wall, for example), the Revenant's Launcher is fully incapable of that. So if that's a thing you like to do, don't just trash your other Rocket weapons the second you've found the Revenant's Launcher. Also keep in mind it has a longer reload time than a Missile Launcher and doesn't have multiple shots: depending on how you like to use a Missile Launcher, the Revenant's Launcher won't necessarily smoothly slot in over a Missile Launcher as a clear improvement.

But overall, it's king of the Rocket weapons.

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Next time, we move on to the final regular 'weapon family': melee weapons.

See you then.