In the context of Pokémon Y, there isn't a single "randomizer QR code" that instantly scrambles the entire game. Instead, QR codes were historically used as an exploit to inject specific Pokémon into a player's PC box.
The "Reverse Type" QR Code:
He reached for the touch screen.
kwsch/pk3DS: Pokémon (3DS) ROM Editor & Randomizer - GitHub pokemon y randomizer qr code