Gastly (ゴース, Ghos) is a creature from the Pokémon games.
Gastly is a dual Ghost/Poison-type Pokémon introduced in Generation I, and is categorized within the Pokédex at #092 as the "Gas Pokémon". It evolves into Haunter at level 25, which can then evolve into Gengar when traded with another player. Gastly and its evolutionary relatives were the only Ghost-type Pokémon in Generation I, and can be found in various games in the wild in haunted areas, caves, and at night.
Gastly's immunity to direct attacks in Smash is likely a reference to the Ghost type immunity to Normal- and Fighting-type moves in the Pokémon games.
As an enemy
Gastly appears as an enemy in Smash Run, appearing somewhat commonly after a minute and thirty seconds have passed.
Gastly slowly floats towards the player, occasionally charging towards them after a random period of time. It causes 3% darkness damage on contact, and flies away if left alone long enough. Gastly is immune to all direct attacks, only taking damage from indirect ones, such as projectiles and other launched enemies.