Mold

The mold F comes in several colors. Each mold causes something bad when you attack it; for example, attacking a yellow mold causes a stun, while attacking a red mold makes you feel hot. If you lack the correct resistance, it is best to let your pet attack the mold.

In both NetHack and SLASH'EM, the mold sometimes leaves a corpse. In SLASH'EM, the corpse might revive itself. "The yellow mold rises from the dead!"