What was the Japan-only Nintendo 64 predecessor to Pokémon Stadium called?

The Japan-only Nintendo 64 predecessor to Pokémon Stadium was called Pocket Monsters Stadium.

Pocket Monsters Stadium was released in Japan in 1998 and preceded the internationally released Pokémon Stadium. It was developed for Nintendo 64 and centered on three-dimensional Pokémon battles, making the creatures from the Game Boy games appear in a console-based battle arena.

The Western Pokémon Stadium is not the same release simply under a translated title. It followed the Japan-only game and was released in Japan in 1999, then in Australia, Europe, and North America in 2000. The Western title used a broader selection of Pokémon and became one of the best-selling Nintendo 64 games.

Another source of confusion is Pokémon Stadium 2. That title is the Western name for a later sequel supporting Pokémon Gold, Silver, and Crystal. In Japan, that sequel was called Pokémon Stadium Gold Silver. The original Japan-only predecessor is therefore Pocket Monsters Stadium.