Gengar

Gengar is a Ghost-Poison Type Pokémon, and is the evolved form of Haunter. This Pokémon hides in the shadows. It is said that if Gengar is hiding, it cools the area by nearly 10 degrees F. Gengar When there is a full Moon, this Pokemon likes to scare people by pretending to be their shadow. Then, Gengar laughs at their fear.

Appearances
In the original games, as well as the GBA games, Gengar can only be obtained through trading to another game. In Diamond & Pearl he appears in the Haunted Mansion, in a room with a painting with eyes that follow you around, very rarely, if one already has the National Dex and a Pokemon game inserted in the GBA slot of the DS. In the Rescue Team version he is a boss in Dungeon 4: Sinister Woods. Gengar appeared in the anime episode, "Night In A Haunted Tower!" and team up with Gastly and Haunter. But in the end, they became silly and happy.