Mancubus

Mancubi are enormously bloated, cumbersome but tough demons that look somewhat like extremely overweight humans. They do have some distinct demon features though - all green eyes, deformed feet, pointy teeth and three pairs of nipples. In addition their arms have been replaced by huge, rapid-firing fireball cannons powered by a generator strapped onto their backs. The game manual describes the Mancubus as follows:
 * The only good thing about fatso is that he's a nice wide target. Good thing, because it takes a lot of hits to puncture him. He pumps out fireballs like there was no tomorrow.

The plural of Mancubus is "Mancubi" rather than "Mancubuses": this is according to John Romero, who was asked as to the correct plural form. This is possibly a hypercorrection, but nonetheless should be considered the correct plural of Mancubus.