Official confirmation that yes, this IS a Pokemon Colosseum reference.
Final details have emerged ahead of next week’s Indigo Disk portion of the Pokemon Scarlet and Violet DLC.
The new trailer includes confirmation that as with the second Pokemon Sword and Shield DLC, older legendary Pokemon (including Rayquaza, Kubfu, and the original legendary bird trio) will be accessible in The Indigo Disk, as well as a further portion of “Area Zero”. Several more minigames were shown as well. The legendaries are tied to the completion of “Blueberry Quests”.
Based on previews of the game, and shown by battle footage, all of the battles in the DLC will be in the Double Battle format as seen in the Pokemon video game championships and one of the gyms of the base game.
A pair of serial code distributions will be live shortly in game; entering “NEWM00N1SC0M1NG” in the Mystery Gift will unlock the mythical Darkrai (available previously through an event download in Pokemon Brilliant Diamond / Shining Pearl or with older save data in Pokemon Legends: Arceus) through December 21, while “SH1NYBUDDY” will give a shiny Lucario until January 4. The former appears to be tied to an upcoming raid event featuring the generation IV / BDSP box mascots Dialga and Palkia.
