Gengar was the first Pokémon shown in the opening scene of Pokémon Red and Blue.
The games begin with a battle animation featuring Gengar and Nidorino before the title screen and the player’s adventure in Pallet Town. The brief scene is easy to overlook, but it became a memorable detail of the original games and their later re-releases.
The matchup also foreshadows the game’s emphasis on Pokémon battles. Gengar is a Ghost/Poison-type Pokémon evolved from Haunter through trading, while Nidorino is a Poison-type Pokémon that evolves from Nidoran♂ using a Moon Stone.
Some players remember Pikachu, Mewtwo, or the player’s chosen starter because those Pokémon are strongly associated with Pokémon’s early imagery. However, the opening battle specifically displays Gengar and Nidorino, with Gengar appearing first in the sequence.