Earth Eater is a boss fought exclusively in the Game Boy Advance and later remakes of the game at the Dragons' Den. It is a very powerful enemy that attacks with a powerful physical attack as well as Megaton Punch which ignores Instant Death immunity.
Earth Eater is an optional boss fought at the Monster Arena after have bred two Area Conquest monsters. It has extremely high physical attack, hitting with a powerful physical attack as well as Megaton Punch, and when on its back, will counter all attacks with Flare. It comes with Auto-Reflect, so most magic attacks are useless against it.
Earth Eater is fought at a secret location to the west of Castle Avalon.