Reserving Slowking.
 
Abomasnow @ Abomasite
Ability: Soundproof
EVs: 8 HP / 68 Atk / 252 SpA / 180 Spe
Quiet Nature
IVs: 0 Spe
- Blizzard
- Wood Hammer / Giga Drain
- Ice Shard
- Earthquake / Focus Blast
 
Slowking @ Leftovers
Ability: Regenerator
EVs: 248 HP / 252 SpA / 8 SpD
Quiet Nature
- Trick Room
- Scald
- Psyshock
- Fire Blast / Ice Beam / Nasty Plot
Mega Abomasnow is an excellent Pokemon with 132 / 132 Offensive stats, an excellent movepool, and a pretty solid STAB combination with two high powered moves in its arsenal.  Due to its abysmal 30 base Speed, Mega Abomasnow is an excellent wall-breaker in Trick Room, as it is the "fastest" Pokemon in the tier under it.  As such, OTR Slowking is the perfect partner to it.  Thanks to Regenerator and pretty solid bulk, Slowking can set up Trick Room multiple times during the match.  Slowking can also switch into powerful Fighting, Steel, and Fire types, while in return, Mega Abomasnow can easily take on Grass and Electric types.
		 
		
	 
Hey friend-- might want to get rid of the 180 speed EVs if you've already got the speed IV and nature at negative. Put the EV in attack maybe? Don't want you skimpt on the voting because of something like that :]
Let's play mind games
Abomasnow @ Abomasite
Ability: Soundproof
EVs: 76 HP / 252 Atk / 180 Spe
Adamant Nature
- Substitute
- Wood Hammer
- Ice Shard
- Earthquake
I know this set is usually SD, but Abomasnow's terrible weaknesses means that it suffers from the same problems as Mega Sceptile, namely survivability. So Substitute is the way to go if you want Aboma to be more than a 1 shot teamslot. Being behind a Subsitute allows you to effectively wallbreak with amazing dual STAB. Good Switches into Abomasnow include 
   Mega Swampert (especially for weather shenanigans) 
 Slowking, 
 Suicune,
  Shaymin, 
 Cresselia, 
 Porygon2, 
 Donphan and more, so you can take a clean hit, set up a Subsitute on the switch out, and go to town!
Hoopa @ Choice Scarf
Ability: Magician
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Hyperspace Hole
- Shadow Ball
- Focus Blast
- Destiny Bond / Thunder Wave
Choice Scarf Hoopa? Eeyore, I know your name is a joke, but are your sets jokes now? Well, sorta. See, at +1, Hoopa sits at 393 speed, which may be lower than most other Scarf abusers, but still outspeeds non-max speed 
 Crobat, Neutral 
  Beedrill-Mega and 
 Sceptile-Mega, Adamant 
 Gatr at +1, Modest Scarf 
 Chandy, Max Speed 
 Houndoom-Mega and 
 Azelf, and 
 Cobalion. All of these mons are threats to TR Hoop/Snow,
 but as TR Hoopa is the only one on SmogDex, everyone will just assume you're TR, especially if you add  porygon2 but being able to play with that expectation really gives you momentum. Especially with Destiny Bond, though that can be changed with Thunder Wave, as either are last ditch efforts if Hoopa is going to go down no matter what, to try and save the match.
Beware of 
 Mega Aerodactyl, as it can outspeed Aboma and Hoopa. Ice Shard is a 2HKO, so unless Aboma is behind Sub, it can be a huge problem. Max Speed 
 Crobat creates a similar issue with access to Brave Bird and decent bulk, though Hoopa can take down non-max speed ones with a well placed Hyperspace Hole. Besides that, most scarfers tend to be a problem, namely 
 Hydreigon, 
 Krook and 
 Nidoking. 
 Doublade also has an easy time with this core, as Hoopa's paper defenses mean even an unboosted Shadow Sneak is an OHKO at any more than 266 Attack (that's 40 EV without a boosting nature, or 160 if you made your Doublade Modest for some trolly reason. Any Plus Nature brings it over that without any EV's at all) and Iron Head hits hard, without Abomasnow being able to answer with anything that could hit for more than 40%.
Also, as 
http://www.smogon.com/forums/threads/oras-uu-teambuilding-compendium-updated-post-stage-4.3532022/ makes very clear, Hoopa is 
 pursuit
   bait
   . Make sure you have a partner who can take on dark types. 
 Florges, 
 Whimsicott, Scarf 
 Mienshao and 
 Infernape make especially good choices with their speed or bulk.
[[pretty pictures]]
EDIT: You don't see much of Hoopa in this match until the end, but had the Fire Blast connected turn 19, and pory2 gone down, Hoopa would have done the same thing. 
forgive the mediocre playing, I decided not to do any fancy predicts, especially when I EQed when Mence came out, because I knew I'd be fine regardless. 
http://replay.pokemonshowdown.com/uu-276634749