Engine bug

There are numerous bugs, limitations and oddities present in the Doom engine.
 * (0,0) respawning bug
 * Arch-vile gluing monsters together
 * Barrel suicide
 * Chaingun fires twice with only one bullet in it
 * Demo desyncing caused by bouncing Lost Souls
 * Demo desyncing caused by menu access
 * Fast doors make two closing sounds
 * Fast doors reopening with wrong sound
 * Flawed collision detection (aka hitscan attacks inaccuracy)
 * Ghost monsters
 * Hall of Mirrors effect
 * Invulnerability colormap bug
 * Lost Soul charging backwards
 * Lost Soul limit
 * Mancubus fireball clipping
 * Medusa effect
 * Monsters fleeing
 * Monsters stuck in doortracks or hanging off lifts
 * Moving platforms limit
 * Noclip bug
 * Ouch face
 * Picked up a medikit that you REALLY need!
 * Player stuck on ledge after restoring savefile
 * Revenant tracers not preserved in saved games
 * Segfault/lightning flash near very tall structures
 * Slime trails
 * Soundtargets not preserved in saved games
 * Stairs you can ascend, but not descend
 * Tag 666 idiosyncrasies
 * Tag 667 idiosyncrasies
 * Turning resolution is lowered when recording demos
 * Tutti-frutti effect
 * Venetian blind crash
 * Visible sprites limit
 * Visplane overflow
 * Voodoo doll
 * Wallrunning