Pokémon Scarlet and Violet may have two forms of shiny Pokémon. A new trailer featuring gameplay footage shows a Jigglypuff in the open world with a golden aura and sparkles all around it. These are not traditional Shiny Pokémon, they're wild Pokémon about to enter their Tera form.
What are shining Pokémon from Pokémon Scarlet and Violet?
It appears as if wild Pokémon in the open world will have the ability to take on their Tera Type form, not just Pokémon fought in raid battles. If you spot a Pokémon with that golden aura, like Jigglypuff, in the new trailer at the 1:40 mark, you can approach and initiate a fight with it. They seem to Terastalize at the beginning of the battle. You'll know if a Pokémon is Terastalized by its crystal-like appearance.
Remember that each Pokémon has its unique Tera Type that might be completely different from its traditional elemental type. In this case, Jigglypuff became a Water-type Pokémon, so your Poison-type moves would no longer have an advantage. With enough damage, a wild Pokémon will return to its traditional Paldean form, and you will be able to catch it.
Looking for more info on Pokémon Scarlet and Violet? Check out Customize your trainer with new expanded options in Pokémon Scarlet and Violet and Meet Wiglett, the Diglett-like Garden Eel species coming to Pokémon Scarlet & Violet here at Pro Game Guides.