Gourgeist is a ghostly Pokémon that has four sizes: Small, Average, Large, and Super Size. Its body is a dark brown pumpkin with a glowing, yellow-orange face carved into the front and a pair of nubby legs. The face consists of two triangular eyes and a grinning mouth; on top of the mouth is a small, triangular cutout for a nose. Poking out of the top of the pumpkin is its slender brown-orange head, which has bright yellow eyes and a small mouth but no visible nose. Gourgeist has long, light pink hair with arm-like tendrils framing its face and bangs that usually cover one eye. On top of its head is a crescent-shaped tuft that is brown on top; this tuft resembles a pumpkin's stem. Their bodily proportions can be passed down to their descendants.
On the night of a new moon, Gourgeist wanders town streets while singing an eerie song. Those who hear its song are cursed. It is also known to sing joyfully while observing prey it has entangled in its arms. Gourgiest's four different sizes determines their target for who they take into the afterlife. Small Gourgeist prefers targeting adults by pretending to be children. The large Gourgiest prefers taking children by pretending to be adults. The Supersize Gourgeist aren't picky and will target anyone.
A Super Size Gourgeist has a different cry from its other three forms, pitched lower than the cry shared by the other forms.
Gourgeist appears to be based on both gourd and modern pumpkin jack-o'-lanterns. Its multiple sizes may be a reference to the tradition of trying to grow the largest pumpkin for Halloween. Its upper body may also be based on the candles within jack-o'-lanterns themselves, with the curl being its wick and its hair-like extensions its dripping wax. It could also be viewed as a mere extension of the shape and the curl on top being its stem. The lower body's different color might also reference the tradition of decorating gourds with paint. It also has potential connections with the famous Japanese story, Yotsuya Kaidan, in which a woman transforms into a paper lantern yōkai with long hair.