The dense fog it creates brings the downfall and destruction of its confused enemies. Ocean currents are the source of its energy.
– Pokémon Sun Pokédex
Tapu Fini is the guardian deity Pokemon of Poni Island. Its unique ability Misty Surge brings up Misty Terrain on the battlefield. It’s the only tapu Pokemon who doesn’t bring up a terrain type that matches is primary type (ie the terrain it brings up is Fairy type, not Water type).
I found Tapu Fini the hardest tapu to catch, because one of its moves it has is Aqua Ring, which means it’s continuously healing itself as you’re trying to catch it. Also, Misty Terrain prevents volatile status, so you can’t inflict a status on it until the terrain wears out.
Stat-wise, it seems more focused on defense, having Def and Sp Def as its highest stats.