There are two versions included:

Stone Imp (original): An Imp variant with no projectile attack. Bit more health than the Imp, but just as slow and can only melee. It is completely immune to electric/lightning and poison based-attacks, has decent resistant to fire-based attacks. but slightly weak against ice-based attacks.

Stone Imp ("hidden"): This is similar to the Stone Imp, except it has a bit more of an ambush tactic. When spawned, it will basically be an exact replica of one of two green marble column decorations. However, when approached, these will morph into Stone Imps with slightly higher speeds and no alert sound to ambush the player.

A very simple monster: Runs towards the player and explodes. Doesn't have much health, and explodes when killed as well.

A very powerful zombie. Not much health, but can almost instantly kill an unwary player close up. Almost useless at long-range. Requires careful placement so it isn't useless and isn't cheap.

Through many slipgates and dimensions this commando has traveled, in order to bring you pain and suffering. He totes a chaingun like your own, and a "tentacle whip" for an arm to strike down any who gets too close to him, unless he's already started his unceasing barrage. Acts like a regular chaingunner that happens to be bigger, meatier, and faster. Can perform a melee attack on you provided you're close enough, and he hasn't started his endless salvo of chaingun fire yet.