Morpeko is a short, chubby rodent Pokémon who can change forms via its signatureHunger 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 waistline. These fur patches form pockets that it can store seeds in. On the back of its body is a pattern resembling a Pikachu's tail that extends from the bottom half of its fur. In its Full Belly Mode, its body is a creamy yellow, 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. The seeds it stores keep Morpeko's hunger at bay due to its small stomach. Unless Morpeko continues to eat its stored seeds, it will become instantly hungry. 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 their hunger is satisfied. The energy within its cheeks also changes from Electric-type to Dark-type. Hangry Mode Morpeko has a wild, brute-like nature while in this form. However, as seen in the anime, once Morpeko is fully fed, it will refuse to eat more food and attack anyone who tries to feed it.
Morpeko has two forms that it switches between with its Hunger SwitchAbility: Full Belly Mode and Hangry Mode. It starts battles in Full Belly Mode and switches between forms at the end of every turn while it is sent out. It is always in Full Belly Mode outside of battle.
Morpeko may be based on the golden hamster with some elements of a guinea pig. Like Morpeko, hamsters are known for biting and exhibiting violent territorial behavior if left untreated, hoarding food, and having incredibly high metabolisms, hence its Dark-type and Hangry Mode. It may also be based on the Norway lemming, as it shares similar color scheme and similar behavior. Its signature moveAura Wheel may be a reference to hamster wheels. Its color scheme may be inspired by the broken color pattern found in many guinea pig breeds. The pockets it stores seeds in probably reference the cheek pouches many rodents have, including hamsters. The fact that is known as the Two-Sided Pokémon and can change into two forms, one of which is violent and evil, may be a reference to Dr. Jekyll and Mr. Hyde, a character written by Scottish author Robert Louis Stevenson.
Morpeko may be a combination of モルモット morumotto (guinea pig) and 腹ペコ hara peko (hungry, starving).