The minion of the Parasite Prince, the Ulcer is a monster with five claws and an underbelly which contains a set of powerful jaws. It also has the ability to spew acid-like slime from its body. After Max was swallowed by his pet iguana, the Prince of Parasites ordered the Ulcer to slime the boy. However, it was blocked by a bone lying on the ground, and hit the Prince instead. The Prince, blindly slicing his sword around, decapitated the Ulcer, killing it. It was later revealed Max had been dreaming, and it is unknown if the Ulcer monster exists or is part of Max's imagination.