Enemies and Items

Commander Keen: Invasion of the Vorticons!
    Commander Keen 1: Marooned on Mars
    Commander Keen 2: The Earth Explodes
    Commander Keen 3: Keen Must Die!

Commander Keen: The Lost Episode
    Commander Keen 3.5: Keen Dreams

Commander Keen: Goodbye, Galaxy!
    Commander Keen 4: Secret of the Oracle
    Commander Keen 5: The Armageddon Machine

Commander Keen: Special Edition
    Commander Keen 6: Aliens Ate My Baby Sitter