What was the name of the Japan-only 1998 Nintendo 64 Pokémon game?

The Japan-only 1998 Nintendo 64 Pokémon game was Pocket Monsters Stadium.

It was released in Japan on August 1, 1998, and was developed and published by Nintendo. The game brought Pokémon battles into polygonal 3D and connected with the Game Boy titles through the Transfer Pak bundled with the cartridge.

Pocket Monsters Stadium was based on Pokémon Red and Green, but technical limitations meant that only 40 of the original 151 Pokémon could be used in its battles. The game had originally been planned for Nintendo’s 64DD peripheral before being converted to a standard Nintendo 64 cartridge.

International naming creates a common mix-up. The later Japanese release Pokémon Stadium 2 was released overseas simply as Pokémon Stadium. That Western Pokémon Stadium supported all 151 first-generation species and contained more features, so many players mistakenly treat it as the first Nintendo 64 Pokémon title. Pocket Monsters Stadium was the earlier Japanese-only release.