The intense monster battles in the Pokémon series took center stage when Pokémon Stadium hit the Nintendo 64 in April of 1999. The game would be released worldwide early the following year, thanks to the international success of the franchise that was established at that point.

The version of the game that would eventually be released internationally was actually the second version of the Japanese release. The first Pocket Monsters Stadium actually released in 1998, and due to the technical limitations at the time, it only included 42 of the then-151 Pokémon potentially available at the time. This version of the game was the result of Satoru Iwata being able to port the battle system from the Game Boy titles to a Nintendo 64 cartridge by reading the Game Boy’s whole source code and converting the programming. The game known as Pokémon Stadium in the U.S. was actually considered a sequel in Japan; it supported the ability to transfer Pokémon from the Game Boy titles (all 151 of them) and had the overall difficulty toned down from the high level of the first release.

Unlike the Game Boy titles, Stadium didn’t have much in the way of a storyline, instead focused on various tournaments and cups for the player to compete in. The closest resemblance to the Game Boy titles is within Stadium’s Gym Leader Castle, in which the player takes on the eight Gym Leaders, then the Elite Four and the Champion, unlocking a battle against the powerful Mewtwo. Once Mewtwo is defeated, higher difficulty levels in the Gym Leader Castle are unlocked.

Though the primary focus of Stadium was on battling against computer opponents, the game also included a number of mini-games that showcased different Pokémon abilities, as well as multiplayer battle options.

Pokémon Stadium received mostly mixed reviews from its debut, with many citing the lack of any sort of story contributing to a feeling of a watered-down Pokémon experience. However, it would go on to sell nearly 4 million copies worldwide, making it one of the best-selling Nintendo 64 titles. A sequel was released the next year, including the creatures from Pokémon Gold, Silver and Crystal and expanding on the gameplay a bit. Though there haven’t been any more Stadium-branded games, Nintendo has continued to release titles in the franchise that have built upon the core gameplay.