The Pokémon Stadium game released internationally in 2000 was made for the Nintendo 64.
Pokémon Stadium is a 3D turn-based battle game developed by Nintendo EAD. It allowed players to battle with Pokémon from the Game Boy games Pokémon Red, Blue, and Yellow by using the Nintendo 64 Transfer Pak.
The international version followed a Japan-only 1998 title called Pocket Monsters Stadium. In Japan, the internationally released game was treated as Pokémon Stadium 2, which can cause confusion when comparing regional titles and release histories.
The game supported battles using all 151 Pokémon from the first generation and also included cups, Gym Leader Castle challenges, and minigames. Its 3D arenas made it a notable visual expansion of the original handheld experience. The Nintendo 64 answer is specific to Pokémon Stadium, not the later Pokémon Stadium 2, which also appeared on the same console.