Unlike most games, evolution in Pokémon Legends: Arceus is done manually. You need to meet certain requirements and evolve them in your satchel. Turning your Hisuian Growlithe, a Fire/Rock regional variant, into an Arcanine follows the same rule.
Hisuian Growlithe evolves the same way a Kantonian Growlithe does: with the use of a Fire Stone. Fire Stones can be found in the Trading Post for 1,000 MPs, by breaking ores and battling the Pokémon that comes out (a Geodude will sometimes drop it, for example), or by treasure hunting using Ursaluna.
Related: What are Effort Levels (EL) in Pokémon Legends: Arceus?
Arcanine has a very high Atk power, so it’s ideal to bump its effort levels for that. You can also consider dedicating resources for its HP and Spd, which are naturally high for Arcanine.
Given its unique Fire/Rock typing, Hisuian Arcanine is one of few Pokémon that is either strong or weak against something. It’s strong against Bug, Ice, Fairy, Normal, Flying, Poison, and Fire but is weak to Ground, Water, Rock, and Fighting. If you chose Oshawott as your starter, know that having Samurott alone will cover half of Arcanine’s weaknesses.
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