10. Transfer Pak
This one gets the nod, despite being something of a one-trick Pony(ta). The Transfer Pak could send data from a Game Boy cartridge to the Nintendo 64 console, and of course, the most significant purpose of this was being able to finally see your beloved Pokemon rendered in glorious polygons.
Modern spoilt whelps may not appreciate the magnitude of this, what with the 3DS titles’ lively models for every single Pocket Monster, but back in the late 90s, it was like seeing a comic book character spring to life. Your once monochrome, pixelated and sedentary Raichu was now up there on the big screen – raining down Thunderbolts from the sky, zipping about with Quick Attack, and subsequently dying, because Raichu kinda sucks like that.
It was pure magic, and though the other compatible titles didn’t come anywhere near this dizzying height (Mario Tennis’ insertion of the Game Boy protagonists was pretty neat), any Pokemon fan knew that the price of admission had already been paid for this humble accessory.