id Anthology Cheats

On the world map, to walk though uncompleted levels, hold tab with the num lock on and walk though the level. You will be able to walk though it like you would a completed level.

Try this in a level where theres a really long drop (The elevator section in Bloogton Towers is perfect). Drop from a ledge, and just as you begin to drop, shoot straight down. As the falling Keen reaches the shot, he will suddenly stand on it, like its a ledge or elevator, but you will still be zooming down at the speed of the shot. Now heres the cool bit: when you reach the bottom, the shot will disappear, but you will be standing just above the ground (sort of in mid-air). Dont move, just aim up, shoot....and now youll be doing the opposite thing. Now Keen will be hurtling towards the top at the speed of the shot. Saves you from all that jumping and grabbing ledges.

In the secret Korath III Base level, climb the red wall at the beginning to find a large number of Bags O' Sugar and a strange fuse. If you are playing the game in Normal or Hard Mode, you can break the fuse with your pogo stick, which will also end the level. Proceed to beat the game to receive a slightly more amusing ending.
If you are playing the game in Easy Mode, the fuse will not break, and you must beat the level normally, and you will not view the alternate ending.