How to find Johto’s Legendary Beasts in Pokémon Scarlet and Violet

The Pokémon Scarlet and Violet games both allow you to catch Legendary Pokémon from previous generations in The Hidden Treasure of Area Zero DLC after you've beaten the story; all you need to do is get the Pokémon's respective Treat from Snacksworth; in Scarlet, you can get the Treats for the Legendary Beasts by completing Solo Blueberry Quests, while in Violet, you need to complete Group BBQs to get their snacks.

Be prepared for their fights; all three of them have a move to change the weather to boost their moves, while Entei knows Swagger, a move that raises your Pokémon's Attack by two stages while confusing it simultaneously.

All three of these Pokémon have the Pressure Ability, which will make you use up your moves faster.

Raikou

Snacksworth's story tells you about how they raced up a mountain, where they ended up seeing the Desert landscape in the north; the mountain in question is where you fought the Bombirdier from the Path of Legends questline; Raikou is at the origin of the river.

Entei

Snacksworth raced Entei across the mines from East Province Area 3; they ended up on the cliffs facing the ocean on the East.

Suicune

Suicune's hint only tells you that it appeared on Casseroya Lake; you can find it on the island west of where you fought the Fake Dragon Titan Pokémon.