Thing types


 * Main article: Thing

Doom, Doom II, Final Doom
These tables include the following columns.
 * Decimal - Type number, in decimal
 * Hex - Type number, in hexadecimal
 * Version - First Doom version that thing appears in:
 * S - Shareware
 * R - Registered
 * 2 - Doom II
 * Radius - Radius, in map units (note that the map "footprint" of a Thing is square, not round, so this is the distance from the center to the midpoint of an edge)
 * Sprite - First four letters of the name of all sprite graphics
 * Sequence - For animated sprites, default pattern through which the animation progresses. "+" indicates that certain gameplay developments (such as a monster being shot) may interrupt this pattern with additional graphics
 * Class:
 * A - Artifact item. Counts toward ITEMS percentage at the end of a level
 * P - Pickup. Player can pick the thing up by walking over it
 * W - Weapon.
 * M - Monster. Count towards kill percentage, hidden when using -nomonosters, respawn in nightmare mode
 * O - Obstacle. Players and monsters must walk around
 * ^ - Hangs from ceiling, or floats if a monster (aside from Commander Keen, who neither moves nor attacks; dead monsters, excepting Lost Souls, fall to the floor when killed)
 * Description

Artifact items

 * 1) Only one of these may be picked up per level, although any additional maps still count against the player's item tally.

Powerups

 * 1) Not picked up if the player's armor rating is at least 200%.
 * 2) Not picked up if the player's armor rating is at least 100%.
 * 3) Not picked up if the player's health rating is at least 100%.

Weapons

 * 1) Not picked up if the player already has one, and is already carrying the maximum amount of the corresponding ammo.
 * 2) Not picked up if the player already has one.

Ammunition

 * 1) Not picked up if the player is already carrying the maximum amount of this type of ammo.

Other
 A certain number of additional objects (such as spawn cubes, rockets in flight, and Spider Mastermind corpses) may not be placed in a level at its outset, but are generated only during actual gameplay.
 * 1) No part of the Icon of Sin is considered a monster by the engine (the boss brain is flagged as an obstacle though).
 * 2) FIRE is used when a spawn cube turns into a monster.
 * 3) TFOG is used while a teleporter is operational.