Commander Keen Series Cheat Codes, and Secrets

Commander Keen is a series of side-scrolling platform video games developed primarily by id Software. The series consists of six main episodes, a "lost" episode, and a final game; all but the final game were originally released for MS-DOS in 1990 and 1991, while the 2001 Commander Keen was released for the Game Boy Color. The series follows the eponymous Commander Keen, the secret identity of the eight-year-old genius Billy Blaze, as he defends the Earth and the galaxy from alien threats with his homemade spaceship, rayguns, and pogo stick. The first three episodes were developed by Ideas from the Deep, the precursor to id, and published by Apogee Software as the shareware title Commander Keen in Invasion of the Vorticons; the "lost" episode 3.5 Commander Keen in Keen Dreams was developed by id and published as a retail title by Softdisk; episodes four and five were released by Apogee as the shareware Commander Keen in Goodbye, Galaxy; and the simultaneously developed episode six was published in retail by FormGen as Commander Keen in Aliens Ate My Babysitter. Ten years later, a homage and sequel to the series was developed by David A. Palmer Productions and published by Activision as Commander Keen. Another game was announced in 2019 as under development by ZeniMax Online Studios.
Cheat codes, console commands, secrets:
Mild cheats:
[C]+[T]+[Spacebar] : Free items
[F8] : Some funny stuff.
[G]+[O]+[D] : God Mode
[Shift]+[Tab] : End level

Hard cheats:
Add to the commandline (for series 1-4):
(This also removes various delays and nagscreens)

Then, in the game, use [F10]+ some letter keys :
[W] Warp to level [E] Restart
[T] Sprite test [Y] Mess up sprites
[I] Free items [S] Toggle slow motion
[D] Record demo [G] Toggle God mode
[J] Toggle jump cheat [C] Stats
[V] Add VLB's [N] Toggle clipping
[M] Memory usage

You may also try adding TEDLEVEL, COMP, NOCOMP.

Episode 4:
In the "Pyramide of moons" get the yellow gem and
open the door then get all of the 12 worms in one
place and they will turn into
a foot climb the foot and enter the secret level.
Cheat codes, console commands, secrets and system requirements for Commander Keen Series free online.

Game description

Game Developer:
id Software (Episodes 1–6) David A. Palmer Productions (2001 GBC game)
Game Publisher:
3D Realms (formerly Apogee Software) (Episodes 1-5)