Evolution works differently in Pokémon Legends: Arceus than it has in previous Pokémon titles. Prior to this game, Pokémon would automatically evolve when they met their certain evolution requirements (reaching a specific level, being traded with another player). In Pokémon Legends: Arceus, Pokémon will still have requirements to meet. But instead of evolving on their own, they will wait until players tell them to evolve, which can be done within the in-game menu.
All Pokémon in Pokémon Legends: Arceus have different evolution requirements, with some requiring evolution items or scenarios in order to evolve. Hisuian Goodra and its pre-evolutions are newly introduced and call the Hisui Region home. Players will have the ability to evolve Goomy into Hisuian Sliggoo at level 40, and Hisuian Sliggoo into Hisuian Goodra at level 50 during rain.
Related: How to evolve Stantler into Wyrdeer in Pokémon Legends: Arceus
Hisuian Sliggoo and Hisuian Goodra gain Steel-typing when evolved from Goomy. This makes them dual-type Dragon and Steel Pokémon, which are very good in battle due to their long list of resistances. Hisuian Goodra is also one of the best Pokémon in Pokémon Legends: Arceus and has impressive stats across the board.
Want to read more about evolution in Pokémon Legends: Arceus? Check out How to evolve Hisuian Zorua into Hisuian Zoroark in Pokémon Legends: Arceus on Pro Game Guides!