Little known trick: to get Heretic to run on a 386, start the
game with HERETIC -DEBUG
 
The following cheat codes work everywhere except the 5th difficulty
level.
 
IDDQD - Instant Death
IDKFA - No Weapons/Ammo
COCKADOODLEDOO  - Turns yourself into a chicken
ENGAGExx   - Level Warp (episode/map)
GIMMEx   - Artifacts (a-j) (1-9) [d does not work]