Morpeko is a short, chubby rodent Pokémon who can change forms via its Hunger SwitchAbility, which alters its appearance. The features shared between the two forms are short, stubby arms and feet; a pair of pink circular cheek pouches; a very tiny nose; two almond-shaped ears with a single fur tuft under each; and a primary body color separating two areas of fur which cover the arms, ears, cheeks, and eyes, and zigzag inward towards its face, stopping at the waist line. These fur patches form pockets that it can store seeds in. On the back of its body is a pattern resembling a Pikachu tail that extends from the bottom half of its fur. In its Full Belly mode, its body is a creamy yellow in color, and its eyes are circular and black with large white pupils. The fur on the left side of its body is black, and on the right side, it is brown. A single bucktooth can be seen protruding from its smiling mouth. While in its Hangry Mode, Morpeko's primary body color turns purple, its eyes become downward-slanting red semi-circles, and its right-hand patch of fur turns from brown to black so that it matches the other side. Its mouth is also constantly formed into an angry snarl.
Morpeko carries around Berry seeds that have been electrically roasted in its pockets. It treats the seeds with care as if they were precious treasures, until it eats them as a snack. Morpeko generates electricity with its cheek sacs; this process consumes a lot of energy, and causes it to become hungry no matter how much it eats. By experiencing prolonged hunger, the hormones in Morpeko shift in balance, and its fur color changes. As a result of intense hunger, Morpeko becomes aggressive, driven into committing all kinds of evil deeds and enacting extreme violence until its hunger is satisfied. The energy with its cheeks also changes from an Electric-type energy to a Dark-type energy. Once Morpeko is fully fed, however, it will refuse to eat more food and attack anyone who tries to feed it, as seen in the anime. Morpeko is the only known Pokémon capable of learning the move Aura Wheel.