Gourgeist is a bipedal, pumpkin Pokémon. Its body is a black pumpkin with two short, stubby feet. There is a face carved into this pumpkin, having triangular eyes and a half-circle mouth, completed with a spike protruding from the top of the mouth. Above this pumpkin is the head, which is tall, slender, and orange in color. At the top of the head is the face, which has yellow eyes and a small mouth with no nose present. The mouth has two sharp fangs, with an absence of other visible teeth. It is completed with its peach-colored hair, which down the sides develops limbs. The hair contains bangs which usually cover one eye. The top of its hair contains a crescent shape, which is peach-colored on the outside and black on the inside. They come in many sizes, the smallest being no more than 2'04" or 0.7m, while the largest are 5'07", or 1.7m. Its colors have switched from when it was a Pumpkaboo, with its lower body being black and its top being pink.
Gourgeist are malevolent Pokémon that catch their prey in their hairlike arms and take delight in their victims' suffering. On moonless nights, they are known to wander through town streets, singing an eerie song that curses its unfortunate listeners. It and its pre-evolution, Pumpkaboo, are the only known Pokémon that can learn Trick-or-Treat.
A Super Size Gourgeist has a different cry from its other three forms, pitched lower than the cry shared by the other forms.
Only Average Size and Super Size Gourgeist can have its Hidden Ability Insomnia. Average Size can be obtained as a Pumpkaboo with its Hidden Ability from the Friend Safari; Super Size can be obtained as a Pumpkaboo from event distributions.
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.