This Gastly is a ghost/poison-type Pokémon owned by Lon.
Gastly is one of three Pokémon owned by Lon that offers "hospitality". When Ash Ketchum and his friends came into the "Scary House", Gastly was trying to scare Ash and his friends along with Gengar and Haunter. Ash and his friends later found out due to Clemont's Clemontic Gear that they were the ones scaring them. 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", Gastly and the rest were preparing to scare them.