Commander Keen in Invasion of the Vorticons

Single-player only. Cheats can turn off achievements and some saves; use them on a spare save.

1. Ctrl jumps, Alt uses the pogo stick and pressing both fires the raygun. Remap them if it's awkward.
2. Turn on two-button firing in the options to make shooting easier.
3. The pogo stick isn't available from the start. Find it early in the game and it opens up higher platforms.
4. Yorps can't hurt you. Shoot them to stun them or jump on their heads, but they'll push you into hazards.
5. Gargs charge when they see you. Jump over them or shoot them before they line up with you.
6. Raygun charges are limited, so pick up every ammo pack and don't waste shots on Yorps.
7. Save on the overworld map between levels. You can't save inside a level.

Tap a secret to reveal it.

• John Carmack's adaptive tile refresh trick made smooth scrolling possible on PCs of the time.
• The team first made a proof-of-concept clone of Super Mario Bros. 3's first level, called Dangerous Dave in Copyright Infringement, to pitch Nintendo.
• Apogee published it as shareware in December 1990, and the team soon founded id Software.
• Tom Hall created Keen and wrote much of the game's humour.
• The trilogy's episodes are Marooned on Mars, The Earth Explodes and Keen Must Die!