Fortegreen is a bean-shaped astronaut of his namesake color, with a visor, two stubby legs, and an oxygen tank on his back. He is an Impostor, equipped with a gun, blade, and tentacles that can emerge from his oxygen tank. His true form reveals a wide mouth filled with small, sharp teeth. Fortegreen is a coldhearted, smart, ruthless, and murderous individual who remains calm and intelligent even in tense situations.