A version of Doom is used to teach Marines to kill.
Marine Doom does indeed exist, but is used to teach "decision making skills," not killing. Marines are taught to kill in much more effective ways, not with video games.
Doom II features a secret level where children are seen hanging from the roof of a concentration camp.
The level is Map 32, Grosse, but it's never said to be a concentration camp and the "children" are actually four Commander Keens and look more like the sprites from Lemmings than people.
Doom is a "murder simulator" that teaches would-be killers to aim for their opponent's head.
In fact, Doom has neither location-specific damage nor any method of aiming for a specific body part. (This lie came from Jack Thompson.)
Columbine shooter Eric Harris' WAD packs include an intricate plan of Columbine High School as a level.
Harris did make Doom WAD map packs, but no such level is known to exist in any of Harris' WADs. While many Doom WAD hosts took the Harris WADs down after Columbine, this was because of their author, not their content. There is no evidence that Harris ever uploaded or attempted to create such a level.
An Atari 2600 port of Doom exists.
A hoax from Electronic Gaming Monthly created by a computer graphics student as an April Fools' prank.
An arcade port of Doom II exists.
The arcade cabinet was a prop created for the movie Grosse Point Blank and no such machine was ever released.
A homebrew Genesis port of Doom exists.
The page's maintainer eventually revealed the homebrew to be a hoax.
Nine Inch Nails frontman Trent Reznor created the sound effects for Doom 3.
Partially true, in fact; Trent was indeed hired, but for some reason the sound effects he created were never used. They later turned up on the internet, and a third-party mod was created to allow them to be used.
The doom guy has pure white eyes
This is only when theinvulnerability power up is collected.
In Map 30 of Doom II before fighting the final boss, Icon of Sin, the game plays a garbled, supposedly "Satanic" message. If played backwards, it turns out to be one of the game's creators, John Romero, saying "To win the game, you must kill me, John Romero."
A sprite of John Romero's severed head impaled on a spike is located inside the hole in Icon of Sin's forehead and can be accessed using the IDCLIP noclipping code. It is in fact the weak point of the boss, but is normally out of view.