The Master Criminal Worm is a very rare enemy in EarthBound, appearing only in Scaraba. It does not drop any money or items, but, upon defeat, gives the most EXP from an enemy in the game. The only two moves it can use are PSI Fire α, its most common attack, or PSI Fire β. It is weak to all PSI moves except Brainshock, and it can only be fought by itself.

Criminal Caterpillars and Master Criminal Worms are the only family of enemies in the game that do not share the same field sprite(i.e. Foppies and Fobbies have the Foppy sprite in the field).