Pokemon Scarlet and Violet's first DLC, The Teal Mask, has arrived, bringing more Pokemon to the game. There are a bunch of returning Pokemon, a few new ones, and a couple of special forms only available in this DLC. One of those special Pokemon is the Bloodmoon Ursaluna, a variant of Ursaluna that is much stronger. You won't find them in the wild though, as they can only be found as part of a special side quest. Here's how to find a Bloodmoon Ursaluna in The Teal Mask.
How to start the Bloodmoon Ursaluna side quest
The quest is started by speaking to Perrin, a woman with green and black hair taking photos in Mossui Town, just west of the Pokemon Center. However, that isn't the only prerequisite for starting this quest. You will need to have caught 150 Pokemon in the Kitakami Pokedex. This is not all of the Pokemon in the area, although it's a pretty healthy chunk.
Luckily, the Kitakami Pokedex features a decent amount of crossover with the regular Paldea Pokedex, so you should have a decent head start. You don't need to finish the main quest to start this side quest, but the four Legendary Pokemon introduced in the DLC cannot be caught without finishing that side quest.