Phantump is a ghostly Pokémon possessing a tree stump. Its black body is wispy with nubby arms. Covering its head is a small, brown tree stump with a wavy branch on each side. Its red eyes are visible through two holes in the stump and its mouth appears on the stump itself. There are two small, green leaves near the tip of each branch. Brewing these leaves can create a curative liquid.
Phantump is created when a spirit possesses a tree stump; it is said that the spirit is that of a child who became lost in the forest and died. This Pokémon's cries sound like the voice of a child or eerie screams. People have become lost following the voice, but Phantump is attempting to make friends. Phantump, along with its evolved form Trevenant, are the only known Pokémon capable of learning Forest's Curse.
Of all the Pokémon that evolve via trading (including with held items), Phantump is the only one whose evolved form can also be directly caught in the wild in the same generation in which it was introduced.
Phantump is probably based on the stump of a kodama, the spirits of trees that sometimes inhabit old-aged trees. It is also similar to other types of tree and nature spirits and deities, such as dryads. Its Shiny coloration is based on the birch tree, known for its gray-and-white bark, with its leaves representing a tree in the autumn.
Phantump may be a combination of phantom and stump.
Bokurei may be derived from an alternative reading of 木霊 kodama, which is a combination of 木 boku (wood, tree) and 霊 rei (spirit, ghost).