Pokémon Stadium could use all 151 species from Pokémon Red, Blue, and Yellow.
The Nintendo 64 game was released in Japan in 1999 and used the Transfer Pak to connect with the Game Boy cartridges. Players could upload Pokémon from the connected games and battle with them in three-dimensional arenas.
An earlier Japan-only Nintendo 64 title, Pocket Monsters Stadium, had featured a limited pool of 40 Pokémon. The internationally released Pokémon Stadium expanded that support to the complete original group of 151 species, which is a frequent source of confusion between the two games.
Pokémon Stadium also included tournament Cups, a Gym Leader Castle, minigames, and rental Pokémon. It was not a conventional story-driven adventure like the Game Boy games; its main focus was battling and connectivity.