Fire Imp

An enemy found only in the Underworld. Imps shoot three vollies of red fireballs which go through walls (and water, and lava). The fireballs can however he hit with a melee weapon to stop them from damaging you and even drop hearts sometimes, allowing skilled players to farm health. Imps will try to teleport to you if you try to get away from them (as soon as they are offscreen. They have a chance to drop Fire flower.

Easily one of the most bothersome enemies, it is not uncommon for three to four fire imps to teleport to a place where it's impossible to hit them and proceed to fire rapidly, making it impossible to do anything.