Back at the docks of Vermilion City, there will be tourist who somehow missed her ship–why, if isn’t Mina, a Trial Captain from the Alola region! If you speak to her again, you can battle her.
Pokémon Trainer Mina
Just like in Alola, Mina uses Fairy-type Pokémon. Jigglypuff is weak to Poison and Steel-types. If you don’t have any strong ones, don’t worry, as it’s not particularly strong. But do beware of Sing, which causes Sleep, and Disable, which stops you using your previous move.
Next up is Mr. Mime, which is Psychic and Fairy. As such, only Poison, Ghost and Steel-types are effective. Poison-types are weak to Psychic, but Mr. Mime only has Psywave, which deals decent damage, but doesn’t deal super-effective damage. Watch out for Light Screen, which halves special damage.