Trevenant is a slender brown tree that stands on six roots bent like spider legs. It has two zigzag indentations wrapped around its body from missing bark. There are two large, crooked horn-like gnarls on either side of its head, and another smaller gnarl on its forehead, with a tuft of green leaves in the middle and a large, menacing dark-red eye below them. Its two arms are held horizontally level, thin upper arms and thick forearms, with missing rings of bark at the elbow and below the shoulder; a black shadow connects them. Each upper arm has a single small spike or leaf. The forearms have a small branch immediately before a large cuff of green foliage at the wrist, connected to hands with three wooden pincer spikes for fingers.
Trevenant is known for being kind toward the other Pokémon residing within its lush leaves, despite its terrifying power. It uses its roots as a nervous system, which allows Trevenant to control trees at will. It will trap people who bring harm to the forest, so they can never leave.