General
- By jumping consistently, speed is accumulated by the jumper. This is called Bunny Hopping.
- If the player types "give health" without a value or with a negative value in the Console, the player will enter a "undead" state. In this state, the player cannot move, nor will they be attacked by Monsters. However, the player will still be able to shoot their Weapon and jump up and down. Command "kill" won't work, resulting in message "can't suicide -- allready dead!" [sic], but the player can be killed by regular means (shot by monster or by standing in acid when the command is activated).
- If the player types "give health" with a value greater than 294911, the player will enter a "undead" state. This difference between this one and the "undead state" of the other Glitch is that the only difference from normal play is the fact that they are tilted on their side. This means that the player can be detected by Monsters and can move around the map, plus do anything else a regular player can do. Command "kill" works in this state as normally.
- A Rotfish counts as 2 monsters in the level kill total. Also, when killed, they continue blocking the player until the last frame of their death animation. This is inconsistent with every other enemy, which becomes nonsolid the instant it dies.
- If a Spawn survives the explosion of a Radioactive Container, the Spawn will remain both alive and invincible. A similiar glitch can also happen with the Fiend if it somehow manages to get killed himself by an explosion from an Radioactive Container usually with the jumping attack, if this happens the Fiend will turn into an "undead" invicible state chasing the player by using his jumping attack without causing damage (And without any sounds). However this is not possible to happen in the original levels since the aforementioned creatures do not an appear in Base levels. This video should serve as a basic demonstration.
- Spawning opponents can be relatively unreliable. The more levels a player plays in succession, the more likely an opponent will not spawn when they should.
- Picking up MegaHealth when your health is already over 100 will stack the rate of health degeneration. There's no limit that can be feasibly reached, so it becomes absurdly fast if several MegaHealths are gotten.
Level-Specific
- In the Grisly Grotto, an Ogre may not spawn if the player doesn't kill a Fiend beside the Silver Door before going after the Silver Key.
- There are four Scrags that never spawn in the Ebon Fortress if the player is on Normal or a higher Difficulty.
- There is a Fiend that never spawns on The Elder God Shrine if the player is on Easy.
- Shub-Niggurath's Pit contains a Nail Trap that fires in the opposite direction.