Doom Roguelike Enemy Analysis: Lost Soul

HP: 10

Protection: 0

Ranged Accuracy: N/A

Melee Accuracy: +12

Ranged Damage: N/A

Melee Damage: 1d3 (+4) Melee

Speed: 100% / 400% (Base/'charging')

Inventory: Nothing.

Experience: 47

Danger: 3

Minimum floor: 6/3/1

Maximum floor: 16

Experience per Danger: 15.66

Unaffected by Acid and Lava on the floor, 50% Bullet resistance, 75% Fire resistance. Leaves no corpse when killed.

Attack Chance: N/A

Has a 'charging' mechanic, wherein a Lost Soul that notices Doomguy from more than 1 tile away will accelerate tremendously but be trapped on its course like a projectile attack until it impacts something unpathable (Doomguy, walls, other enemies, etc), or takes damage, or travels a total of 15 tiles in this state. Any of these will interrupt the charge behavior, reducing it to its normal speed and allowing it to move and act freely.

Notice that Lost Souls have triple the Danger of a basic Former Human while providing only barely over twice as much experience. Former Humans thus provide 23 experience points per unit of Danger, while Lost Souls provide 15.66~ experience points per unit of Danger. Enemies broadly have a variable rate of Danger-to-experience-points, but the Lost Soul stands out for two reasons; firstly, it has the lowest ratio you'll see on enemies. It's tied with a few other enemies for this low ratio, but that gets to the second point: the Lost Soul is the only one of these enemies with the lowest possible experience-from-Danger ratio that can be selected by the 'cave' level variant, which is always filled exclusively with a single enemy type (Well, almost always), and furthermore has only 67% of standard Danger. Lost Soul caves are thus uniquely janky; they noticeably lower the player's expected experience payout from a floor, and so a run can end up noticeably behind the curve of power because one or more Lost Soul caves generated. (A Lost Soul cave generates less than 50% of the experience you'd get out of a standard floor that happened to only generate basic Former Humans)

As a concrete example: if you're playing on Ultraviolence and you hit every Special Level and kill 100% of enemies on every floor, normally you'll show up at the Phobos Anomaly at Level 6 and so can have your Mastery online for it. (Sometimes you'll even show up at Level 7, and so have your Mastery online even if it's one of the late ones) A run that has a couple Lost Soul caves generate before that point -which is unlikely, but I've had it happen a few times!- is worryingly likely to arrive at the Phobos Anomaly at only Level 5. That can be crippling, depending on what build you're developing, possibly getting a run killed that ought to have breezed through!

The window on this problem is thankfully small as cave floors rapidly stop being allowed to pick Lost Souls, but the potential to foul up early levelup checkpoints is the biggest problem overall anyway; having a Lost Soul cave deny you a bunch of experience when you're already Level 12 is generally less harmful than a Lost Soul cave slowing your growth when you're Level 3 or 4.

Anyway, Lost Souls are our first example of an enemy lacking ranged attacks. Like every such enemy, they compensate in part through excellent ability to close the distance coupled with having a notable ability to shrug off punishment on the way in, though compared to other examples Lost Souls put the emphasis more on speed than survivability. If it weren't for their excellent resistances to Bullet and especially Fire damage, they'd be no tougher than a Former Human, and indeed they can be trivially torn apart by Shotgun fire even at long range. (You'll usually need to shoot twice, but only twice)

They do have those resistances, though, so they can be a pain to kill for runs focusing on Pistols or to a lesser extent rapid-fire weapons, and notably are actually pretty prone to surviving rocket attacks. (By which I actually mean: even on Angel of Max Carnage, a direct hit from a Rocket Launcher will do exactly 9 damage, leaving a Lost Soul alive, albeit barely) This latter point is significant since it's pretty common to end up fighting Lost Souls in swarms, and rocket weapons don't do as much to help as you might hope. Indeed, firing a rocket into a mob of Lost Souls often ends up spraying them all over the place, still alive, making it more of a nuisance to finish them off! Their resistances especially make them a pain to Angel of Marksmanship runs; a Lost Soul cave can be all but a death sentence to such a run if it happens early.

The Lost Soul 'charging' mechanic also makes for a good time to talk about a general AI quirk: 'locking on'. I've referred to this several times in an unclear way, but the short version is that just because an enemy can see Doomguy, that doesn't necessarily mean they're interested in him. Enemies are often perfectly happy to wander multiple turns in a row in view of Doomguy, not attacking and not moving toward him! On ranged enemies, this is often obscured by the fact that even once they're 'locked-on', they only have a chance of deciding to attack: it's not immediately obvious the difference between 'ranged enemy wandered randomly and happened to choose to move closer to Doomguy' vs 'ranged enemy wants to attack Doomguy, but failed its check for that and so elected to advance instead'.

With Lost Souls, the distinction is much more obvious, because a Lost Soul will almost always respond to 'locking on' to Doomguy by immediately entering 'charging' mode, whereas if they're not currently interested in Doomguy they'll always move about at their regular speed. (I say 'almost always', because I occasionally see a Lost Soul that's 1 tile away clearly not engage the charging mode in response to being attacked, and occasionally it takes a turn for them to do so in cases where lines of fire are funky)

In general, this 'locking-on' behavior has some implications as far as what's good play, in that for example it's generally best to fire on enemies you've previously injured and/or who have already launched attacks at you over enemies where neither event has occurred. If you've already provoked a Hell Knight, attacking a so-far-uninvolved Imp in vision will assure that it attacks you if it survives the attack, whereas ignoring it might lead to it continuing to wander about blithely. Conversely, part of the value of techniques like 'radar-shooting' is to provoke enemies into 'locking-on' to Doomguy, making them more predictable: enemies who are 'locked-on' pursue Doomguy precisely even if they don't have sight of him!

Though this is a temporary state. If 5-ish turns of pursuing Doomguy pass without further provocation, most enemies lose track of him and have to be re-provoked if you want to eg lure them to melee range and they don't have vision on Doomguy. (If they do have vision on Doomguy, they'll generally keep pursuing even if enough time has passed that the original provocation was 'forgotten')

I'm not entirely sure how this 'locking-on' behavior works otherwise: I'm quite certain enemies can react to visible buddies being hurt and killed by seeking out Doomguy, but the rules for this are pretty unclear to me, where sometimes I shoot an enemy in view of another enemy also in view and that second enemy continues wandering without regard to me, and other times I have a Tracking Map showing me that an enemy out of my sight is being provoked by me hurting an enemy that's in its own vision range. The main other broad wrinkle to it I can confidently point to is that various enemies 'hunt the player precisely', meaning they are always pursuing Doomguy and open to attacking him even if they've never seen him and have never been hurt by him, making all this 'control when you provoke them' stuff a moot point. (A sub-point to this is that floor events can instill this 'hunts player precisely' behavior in any enemy)

In the case of Lost Souls in particular, the fact that they speed up enormously when charging Doomguy makes them more extreme than most melee-only enemies about 'deal with the ones you've provoked before you provoke others'. A Pinkie Demon who hasn't noticed Doomguy yet may still wander directly toward him multiple turns in a row at full speed, albeit this is unlikely. A Lost Soul who happens to keep wandering toward Doomguy is at least covering way less ground over that time than it would if it was actually charging.

On a different note, Lost Souls are surprisingly lethal. I describe them as 'nibbling' on Doomguy, but +4 damage is only 1 point less than Pinkies get! 5-7 damage adds up fast if you let Lost Souls swarm you. I call it 'nibbling' mostly because melee builds normally have enough resistance and Protection to shrug it off (Berserk's resistance already knocks their max damage roll to 2.8, for example), while ranged builds can generally avoid being bit in the first place. But when you're doing stuff like considering hitting the City of Skulls while playing Angel of Marksmanship, they may well tear Doomguy to ribbons in no time flat!

Also, it should be pointed out that Lost Souls share their pain noise with Pinkies and Hell Knights. This is probably the most regularly problematic case of shared audio, as there's some pretty stark differences in the threat profiles presented by these three, and it can be very misleading when blind-firing. Provoking a Lost Soul or Pinkie that's out of sight when you're standing in the open across a river of Acid is a very different scenario from provoking a Hell Knight in such a situation!

As an aside, 0.9.9.8 tweaked how Lost Souls animate when charging so it plays out differently from normal enemy movement animation. I appreciate this for how it makes the existence of the charging behavior easier to deduce. It'd be nice if they had new sprites reflecting the direction of the charge -having the flame trail behind them, for example- to be even clearer, but this is a nice improvement.

Actually, in general 0.9.9.8 brought with it art changes. Most enemies specifically got a second sprite that's very slightly different from their existing sprite, with them alternating the two to get a bit of animation going (It helps more than you might expect, honestly, making it much harder to overlook enemies in view), but a few had their sprites completely redrawn. The Lost Soul is the first such case we're getting to: in all such cases, I have the original sprite on the left and one of the new sprites on the right.

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Next time, we cover pinkie Demons, the much more dangerous melee threat that mostly enters rotation faster than Lost Souls.

See you then.