Revenant

Revenants are monsters introduced in Doom II. They have the form of walking skeletons that fire seeking missiles (only about a half of them are target seeking, the ones with the smoke trails). They can also attack by punching like karate.

If a Revenant is within 196 units of its target it won't use its projectile attack unless attacked and hurt, which makes it counter-attack with its missile.

According to the manual:
 * Apparently when a demon dies, they pick him up, dust him off, wire him some combat gear, and send him back into battle. No rest for the wicked, eh? You wish your missiles did what his can do.