Lost Soul

The lost soul was first introduced in Doom's second episode, The Shores of Hell, but can be seen as early as E1M1 on the PlayStation and Saturn ports of the game where they can be spawned by a pain elemental hidden in a secret corridor.

Doom II made additional use of the lost soul by utilizing it as the projectile attack of the new pain elemental monster. The Doom manual gives this description of lost souls: "Dumb. Tough. Flies. On fire. 'Nuff said."

Physical appearance
The lost soul is a flaming, flying skull with two horns, orange eyes with yellow dots for pupils, and very sharp teeth. In the PlayStation and Saturn versions of Doom, lost souls appear to have more defined brows.

Combat characteristics
Arguably one of the most frustrating enemies in the Doom games, lost souls silently float at a leisurely pace until they decide to attack, at which point they launch themselves towards the player at high speed with a hissing breath sound, often the first audible warning of their presence. If they miss, they will continue careening through the air until they hit a wall or other object.

It is uncommon to find a lost soul on its own — they are more often found in groups. They also make no sound when alerted, sometimes surprising careless players because of this.

Lost Souls simply explode when destroyed. Because of this, the lost soul does not normally respawn when the Nightmare! skill level is chosen or the -respawn parameter is used. The lost soul will, however, leave a small pile of gibs if it is crushed whilst dying, in a similar manner to the pain elemental. Unlike the pain elemental, its crushed gibs cannot be resurrected by an arch-vile.

Note that the lost soul sprite always remains fully bright in the same way projectiles and lamps are lit up, to represent the light emitted by their flames.

In Doom II and Doom v1.666, lost souls were modified to no longer affect the player's kill score, so it is possible to achieve 100% kills without destroying any lost souls found in a level. This was undoubtedly due to the addition of the pain elemental. However, in later ports, such as the PlayStation and Saturn versions of Doom, they are considered part of the kill score, easily pushing the kill ratio past 100% if pain elementals are also present.

Tactical analysis
The player can stop a lost soul's charge by shooting it while it is attacking. Because of their 100% pain chance, it is often safer to use the pistol against them, rather than the slower-fire shotgun, so the lost soul will not have enough time to retaliate. Also, lost souls will stop when they cross an object in their charge path, such as a shotgun or a medikit, which stops them as if the objects were a wall. Using rockets against groups of lost souls is strongly discouraged, as there is a considerable chance that a lost soul will suddenly fly towards the player, causing one of the rockets to explode too close to the foolish marine, resulting in serious blast damage. However, the rocket launcher is particularly effective against large crowds of lost souls but one must exercise extreme caution should they employ the weapon against these airborne targets.

In early versions of Doom (pre 1.9?, it happens in 1.666), the Lost Soul also had a special ability to dodge rockets; If a rocket was within a certain distance of it and it wasn't already attacking, the Lost Soul would sometimes "sidestep" by darting left or right very quickly (it would quickly turn 90 degrees and then perform its distance attack in that direction for a fraction of a second).

Lost souls will target other lost souls. One unique characteristic of the monster type is that after they attack, they do not retain their target, and instead pursue the player, unless hurt by their previous target. This makes them somewhat unreliable when a player provokes and attempts to sustain monster infighting, or at least unpredictable in such situations.

Pre-release version
In the available pre-release versions of Doom, lost souls are grey, non-flaming and use a "psychic" attack, facing the victim and flashing for a moment, delivering a hitscan attack at the player. These early lost souls leave behind a pile of floating bones. The invulnerability powerup has a face similar to that of these early lost souls.

There exists a thing type in the final version of the game, named MT_MISC65 (called "Dead Lost Soul" in DeHackEd), which produces the last few death frames of the lost soul. This dead lost soul was evidently left over from earlier versions of the game where the monster did leave a corpse, such as in the press release beta. This thing would have served the same function as the other decorative corpses (the imp and the zombieman corpses, for example). Regardless, it is not possible for an arch-vile to resurrect a lost soul even if it is crushed while it dies (which leaves a puddle of blood as its corpse), as it does not have the necessary resurrection frames.

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 * 1) This table assumes that all calls to P_Random for damage, pain chance, and blood splats are consecutive. In real play, this is never the case: counterattacks and AI pathfinding must be handled, and of course the map may contain additional moving monsters and other randomized phenomena (such as flickering lights). Any resulting errors are probably toward the single-shot average, as they introduce noise into the correlation between the indices of "consecutive" calls.
 * 2) Assumes that direct hits are possible, which does not occur in any stock map.

Appearance statistics
In classic Doom, the lost soul is first encountered on these maps:

The IWADs contain the following numbers of lost souls:

Doom RPG
In Doom RPG, the lost soul appears as a class of monster. There are three variations, identified by color:


 * Phantom (green)
 * Lost soul (normal colors)
 * Nightmare (blue)

Lost souls can move three panels in a single turn instead of one, and will attack automatically once they are in an adjacent panel to the player, even if it has already moved. It attacks three times consecutively and can be damaged by the fire extinguisher.

Doom 64
These variations of the lost souls look somewhat different, are slightly transparent, and there is fire only on the top of their skulls (the fire is also transparent). They are also much more aggressive than their PC counterparts, with faster and more repeated attacks. It is also physically weaker than their PC counterparts and can be felled with a single shotgun blast (not unlike the variants found in the PlayStation and Saturn ports).

The Lost Souls in Doom 2016 (react more closely to these kind but explode on contact with the player)

Trivia

 * The lost soul is the only monster in Doom to not make any sound when alerted.
 * The lost soul is one of two monsters that do not leave a corpse (the other being the Pain Elemental).