Flash Fire

Flash Fire is an ability in Polished Crystal that makes the user immune to Fire-type moves and boosts the power of its own Fire-type moves by 50% when hit by one. This ability is particularly useful against Fire-type attacks, as it not only negates the damage but also enhances the user's offensive capabilities in return.

You can find this on quite a few fire type Pokémon including Growlithe, Vulpix, and Houndour evolutionary lines. If you evolve an Eevee into Flareon, it will also have a chance of having this ability as well!

When your lead Pokémon has the ability Flash Fire, wild Pokémon have a 50% chance to be Fire type... if available on that route, that is!