Mothim is a moth-like Pokémon with two pairs of wings, one larger than the other is. The wings are primarily tan with an orange, oval marking on each. The tips of the wings split into small, orange squares; there are three on the large pair and two on the small. Mothim has orange eyes with gray, orange-tipped antennae running along the edges before extending and widening above its head. Its body is black with a patch of orange on the underside and a gray stripe down its back. Four gray legs and a small black tail that splits into two squares are also present. Mothim is a nomadic, nocturnal Pokémon that always remains on the move, searching for honey and nectar. Instead of gathering honey on its own, it raids the hives of Combee. It is a male-only species, with Wormadam as its female counterpart.
While Mothim represents the adult stage of a bagworm moth, which only fully matures if it is male, both its appearance and honey-thieving tendencies suggest that it may draw more inspiration from death's-head hawkmoths. It may also draw some inspiration from the Crambidae, a family of moths known for their nose-like palps.