Sounds like a disgusting thing on hyper offence if you ask me, go for Eject Button and then short of Whirlwind/Roar or replacing the terrain the opponent can't use any nasty status plays on your subsequent grounded sweeper - with things like burns, toxic and priority TWave not being an issue. If you give it Defog and bulky defences, it can come in later and hopefully clear away troubling hazards or trap for a favourable switch with Whirlpool/Mean Look (Mean Look might be better as it doesn't damage the opponent, guaranteeing you set up with your sweeper rather than the opponent faint). Even without the Eject Button gimmick, the trap and switch is fairly insane (and, I think, what it's intended for as it learns both on level up).
Something like:
Tapu Fini @ Eject Button/Leftovers
Ability: Misty Surge
EVs: 252 HP / 4 Def / 252 Spe
Timid Nature
- Mean Look/Whirlpool
- Taunt/Haze (to stop opposing set up sweepers)
- Defog
- Coverage
Personally, I think this set from now on should be called the Awesome Jojobobo Set, or the AJ set for short. This kind of facile trapping will be troublesome for OU, if GameFreak had given it something like Recover I think it would easily have been an Uber mon as water fairy typing is pretty solid defensively.