This Gengar is a ghost/poison-type Pokémon owned by Lon.
Gengar is one of three Pokémon owned by Lon that offers "hospitality". When Ash Ketchum and his friends came into the "Scary House", Gengar was trying to scare Ash and his friends along with Gastly and Haunter. Ash and his friends later found out due to Clemont's Clemontic Gear that they were the ones scaring them when Gengar was playing the piano. Lon then explained everything about the "Scary House". When Ash and his friends found a notebook that belonged to Lon, it was revealed that three Ghost Pokémon were the ones that made the house scary in Lon's days. When Team Rocket arrived at the "Scary House", Gengar and the rest were preparing to scare them.