Iron Shell Pupa is a pale-yellow, insect-like Pokémon in its pupal form. It has a round head and black triangular eyes, with sickle-shaped arms emerging from the middle of its body.

Iron Shell Pupa is the pupal stage that precedes evolution into an adult. To avoid detection by predators, it hides behind leaves or in the crevices of large tree branches, remaining almost completely still as it waits for the moment of evolution. Although it is a pupa, it can still make slight movements; if threatened by an enemy, it will extend its venomous stinger to attack and harden its exoskeleton as a protective measure. Over time, its body gradually matures, becoming increasingly warm as it prepares diligently for evolution. Despite being soft on the inside, its exoskeleton grows progressively harder.