So. This is Hoopa’s new alt form. Ignoring the fact that we’ve never even gotten our hands on a regular Hoopa yet, let’s talk about what the datamining has revealed about this thing so far:
Hoopa-H’s stats are geared to make it hit really hard, while being able to soak up special attacks. Hoopa learning Nasty Plot, combined with Psychic and Hyperspace Fury, packs quite a wallop. Just try avoiding trying to trade blow-for-blow with anything physical for too long, since you’re probably not going to outlast OR outrun them.
As a dark-psychic, its only weaknesses are x4 weakness to bugs, and x2 to fairy. Since the majority of the more popular bug moves are physical (X-scissor, U-turn), Hoopa-H might not fare well against anything with access to those moves (Genesect).
Like with the original Hoopa, Magician offers the possibilities for all sorts of shenanigans. Since it changes via a key-item, you can still put items on it while in Hoopa-H form. (If you do, I recommend using something creative to get around that mediocre speed, though.)
More info and strategies about Hoopa-H should be uncovered after ORAS is released. Hopefully, there will be an event or something that lets us get our hands on Hoopa soon.
If the internet is to be believed, datamining the new Pokemon ORAS demo has revealed the stat distribution for a good number of the upcoming mega pokemon, along with some other (tentative) info like new moves and move tutors
Your guess about the mystery guy on the bottom is as good as mine.
Which mega will you put in your team?