Pokémon
Pokémon Scarlet and Violet DLC, How to find the returning Legendaries
You don’t have to trade to get them all, but you still need to interact with other players.

Pokémon Scarlet and Violet’s DLC, the Hidden Treasure of Area Zero gives players the opportunity to catch the legendary Pokémon from previous games, and luckily, none of them are version exclusives, not exactly anyways, you still have to play with others.
How to unlock the legendaries?
You can’t go and find them as soon as you enter the DLC, for you to be able to find and catch them you have to talk with Snacksworth, a gentleman that appears in the Blueberry academy entrance once you finish the DLC’s main story, he’ll give you a Treat preferred by a legendary at random, depending on how many Blueberry Quests (BBQs) and which kind you have completed (single or Group).
Version Exclusives?
There are no version exclusive legendaries this time, you can catch all of them so you become their Original Trainer, but there is a catch, 13 Pokémon are available on Single player, and the other 12 are locked behind multiplayer.
Which Pokemon are for Single Player and which are for Multiplayer?
Both games
Here is how the Pokémon are separated for each version, Aticuno, Zapdos, Moltres, and Kubfu are available for both versions regardless of you playing on single-player or multiplayer, while Rayquaza, Kyurem, and Necrozma are locked behind multiplayer for both versions.
Scarlet
Pokémon Scarlet has Raikou, Entei, Suicune, Ho-Oh, Latios, Groudon, Reshiram, Solgaleo, and Glastrier as rewards on Single player, but Violet players can still get them if they play on multiplayer and complete Group Quests; you don’t need to play with the other version, only with other players.
Violet
Pokémon Violet has Lugia, Latias, Kyogre, Cobalion, Terrakion, Virizion, Zekrom, Lunala, and Spectrier as rewards on Single-player, but Scarlet players can still get them if they play on multiplayer and complete Group Quests; you don’t need to play with the other version, only with other players.
Can I Shiny Hunt these Pokémon?
Sadly, all 25 of the returning legendaries are Shiny Locked, meaning that no matter how many times you reset your game, nor you restart your whole file, these Pokémon will not be any other color than the original.