Shiny hunters are going to have a field day with the new map and Pokémon in Scarlet and Violet’s The Teal Mask DLC, however, there is one key factor that will end up disappointing players who want to try and find colorful variants of some specific species.
According to a datamine of SV’s version 2.0.1 update, any static encounters in the DLC are Shiny-locked—including Gift Pokémon. This means if you receive a Pokémon from an NPC or are guaranteed to encounter that Pokémon every time you meet specific requirements, it can’t be a Shiny.
This applies to a sizable list of Pokémon most players would love to get ahold of as Shinies, including Ogerpon, Okidogi, Munkidori, Fezandipiti, and the new Bloodmoon Ursaluna. The static Milotic and Ariados encounters that you can find are also Shiny-locked.
As for Gift Pokémon, the Hisuian Growlithe and Sinnoh Starters you can receive are all barred from being Shiny too. Ironically you can get a Shiny Munchlax as a gift somewhere in the DLC, according to the files, so it is the lone exception to this disappointing development because it will always be Shiny and have a Crafty Mark.
All this means is those Gift and static Pokémon can’t be Shiny, which sadly locks you out of getting Ogerpon, Okidogi, Munkidori, Fezandipiti, and Bloodmoon Ursaluna as Shinies completely as of the DLC’s release. You can still get every other Pokémon and their Shinies through other means, however.
If you want a Shiny Sinnoh Starter, you will just have to catch one in another game like Legends: Arceus, and transfer it over through Pokémon HOME, or start breeding them to try and hatch a Shiny. The same applies to Hisuian Growlithe.
You can Shiny hunt wild Spinarak, Ariados, and Feebas to get their Shinies while playing the SV DLC since they appear throughout the map outside of those static encounters—though I have not seen a Milotic in the wild during my time playing just yet, and Feebas is a very rare spawn, as usual.