Where can you find the legendary Pokemon in crater battle arena?

You can't find any legendary Pokemon in the Crater Battle Arena. That's because the Crater Battle Arena is a location from the Pokémon Trading Card Game, not from the main series games.

Legendary Pokemon appear in various locations in the main series games, but their locations vary depending on the game. To find out where you can encounter a specific legendary Pokemon, it's best to consult a guide for the particular game you're playing.