>>21512113160 base Attack.
170 base Special Attack.
Plenty of moves to abuse on both ends.
Enough Special bulk to take a hit and force a switch.
Enough status moves to abuse that can fuck over most would-be switch-ins.
Enough raw power to explode most would-be switch-ins.
Any team that isn't 100% balls-out hyper offense is going to have a point where Hoopa-H can come in and start wrecking shit. Even then, Trick Scarf Hoopa-H is still a threat to offense as it can even come in on things like LO Landorus-I, LO Greninja, and Specs Keldeo's Hydro Pump, survive a hit, and KO on the next turn.
>>21512493There's probably going to be pure physical sets as well. Choice Band + Knock Off + Gunk Shot/Punches/Zen Headbutt/what have you is punishing. There's also the option of Trick, Thunder Wave, Destiny Bond, Magic Coat, and Skill Swap because Magician is useless and OU is filled with things that suddenly shapeshift into fodder without their Abilities.