Pokémon Sword and Shield were released with 436 Pokémon in the game’s code. Only 401 of these are initially available for players to catch in the game. Recently, however, players have reported seeing the other 35 in Max Raid Battles.
So, it seems like folks have managed to get access to non Sword and Shield Pokémon in raids, before they're officially available.
I just received a Squirtle in a Sword and Shield Surprise Trade.
— Laura Kate Dale (@LaurakBuzz) February 11, 2020
It seems like hackers have found ways to put these 35 unreleased Pokémon into Max Raid Battles. Players can then see or join these Max Raid Battles through the Y-COMM. It might not be advisable to do this, however, as Nintendo will likely look to punish those who abuse this.
Players have reported sighting raids with Solgaleo, Reshiram, Mewtwo, Necrozma, Marshadow, Squirtle, and various other creatures that don’t exist in the Sword and Shield Pokédex. These are all part of the 35 unreleased Pokémon in the code.
How to spot these raids
Spotting these hacked raids should be pretty easy. If the Pokémon isn’t part of the Pokédex in Sword and Shield, it is hacked. If you haven’t completed the Pokédex or don’t know, it’s probably a good idea to avoid the raid. Sometimes you can tell what’s in the raid by the outline in the Y-COMM, check whether the creature is in the Pokédex before joining the raid.
If you do wind up battling or catching one of these unreleased Pokémon, do not use it in competitive play. This will almost certainly result in a ban. To be safe, it’s probably a good idea to just release it. Always be sure to check whether what you caught is in the Pokédex before using it if you are unsure.
— Jay ⚔️🛡 (@Jay_Recklesss) February 1, 2020
When Pokémon Home comes out later this month, there is a good chance that some of these Pokémon will be released. Be sure to stay tuned to see which Pokémon will be legal in the game and competitive play when that time comes. Until then, be wary of the raids you join and the Pokémon you use.