While the multiplayer Switch Online Game Boy Advance games all support wireless multiplayer in place of physical Game Link Cables, it’s particularly important for these games because they were the first Pokémon titles to support any kind of wireless multiplayer, even before the Nintendo DS made built-in Wi-Fi connectivity a standard console feature.
FireRed and LeafGreen were two of just a few dozen GBA games to support the Game Boy Advance Wireless Adapter, a bulky, standalone accessory that latched to the top of the system and plugged into its Link Cable port. The initial releases of the games actually included the wireless adapter as a pack-in accessory, which had to be supported by the game you were playing and couldn’t just work as a stand-in for a physical Link Cable in older games.
With the wireless adapter plugged in, up to 30 players could congregate in the game’s “Union Room” to do battles and trades—but given that Nintendo also recommended players stand within 10 feet of each other for the best experience, a 30-person Union Room would have gotten pretty crowded in real life.
FireRed and LeafGreen are adaptations of the original 1996 Pokémon games for the old black-and-white Game Boy. The names reference the original Japanese releases, Red and Green. A third version of the game with updated graphics and other changes, called Pokémon Blue, was released in Japan in late 1996, and this was the version that was localized and released in the US as Pokémon Red and Blue in 1998.
A final version of the base game, Pokémon Yellow, was released in Japan in 1998 and in the US in 1999, with some changes that tracked the plotline of the Pokémon anime (most prominently, mandating that players select an un-evolve-able Pikachu as their starter Pokémon). Most of the changes specific to this version of the game weren’t included in the FireRed and LeafGreen remakes.