Start the game with the command-line parameter '-tedlevel ##'. ## equals the episode and level numbers minus one.
Difficulty Select
Start the game with the command-line parameters '-baby', '-easy', '-normal', '-hard'.
Infinite Lives
Start the game with the Level Select and Difficulty Select command-line parameters.
Full Health, Ammo, Keys, Chain Gun
During gameplay, press L + I + M.
Commander Keen Cheat Message
During gameplay, press A + B + T.
Debug Mode
Start the game with the command-line parameter '-GOOBERS'. When in the game, press Alt + L-Shift + Backspace. Now during gameplay, press any of the following:
Tab + G = God Mode
Tab + W = Select Level
Tab + I = Free Items
Tab + X = Extra Stuff
Tab + S = Slow Motion Effect
Tab + B = Change Border Color
Tab + C = Display Number of Items, Doors, Actors
Tab + E = Skip Two Levels
Tab + F = Displays Coordinates
Tab + H = Lose Health
Tab + M = Display Memory Usage
Tab + P = Pause without Message
Tab + Q = Exit Game
Tab + T = View Graphics and Play Sounds
Tab + V = Add Extra VBLs
100% Health, Full Ammo, Largest Gun, All Keys
During gameplay, press M + L + S.
Freeze Enemies
Save your game as 1234. Sometimes a door or button will be stuck, so remember to quicksave.