There are many enemies in the Commander Keen games. All are unique.
Keen 4
Bounder.
Bounder is not harmful to the touch, and can actually help you reach otherwise impossible-to-reach items. However, Bounder can be annoying at times.
Lick.
Lick is a dangerous, fast-moving enemy. While Lick is not harmful to the touch, he spits fire at you which is.
Mimrock.
Like Big Boo in Mario games, this fearsome enemy will move and jump at you when you look away, but when you look at it, Mimrock looks like a harmless rock. Beware of rocks that are in awkward positions, such as teetering on cliff edges- they're probably Mimrocks.
Poison Slug. These enemies are doubly dangerous- harmful if you touch them, or the slime they leave behind them!
Keen Dreams
To the Pyramid of Gnosticene Ancients
To the World of Classic Games