Engine bug

There are numerous bugs, limitations and oddities present in the Doom engine.
 * (0,0) respawning bug
 * Barrel suicide
 * Demo desyncing caused by menu access
 * Fast doors 2 x closing sound
 * Fast doors reopening with wrong sound
 * Flawed collision detection (aka hitscan attacks inaccuracy)
 * Ghost monsters
 * Hall of Mirrors effect
 * Invulnerability colormap bug
 * Lost Soul limit
 * Mancubus fireball clipping
 * Medusa effect
 * Noclip bug
 * Picked up a medikit that you REALLY need!
 * Slime trails
 * Soundtargets not preserved in saved games
 * Tutti-frutti effect
 * Wallrunning
 * Visible sprites limit
 * Visplane overflow
 * Voodoo doll