There's very little need for EV training when your team is at level 82+, since this is in game, even if Benga is tough. If you plan on using them later in competitive play, then EV training wouldn't be a bad idea. I'll add EVs for the movesets anyway.
I would suggest Haxorus; Emboar is a slow sweeper with good HP, while Haxorus is a fast & strong sweeper with good boosting moves.
Emboar @ Leftovers
Ability: Blaze
EVs: 252 HP, 252 Atk, 4 Def
- Flamethrower/ Fire Punch
- Stone Edge/ Rock Slide
- Brick Break
- E-Quake (filler move)
While this set isn't appealing, let me explain. Since this is Black Tower, you won't be able to use healing items. Flare Blitz will only shorten the life span of your Emboar. Your two other options are Flamethrower or Fire Punch, since Fire Blast has too low a PP. Emboar has a decent Sp. Atk base of 100, so Flamethrower is a viable option.
Haxorus @ Draco Plate/ Dragon Fang
Ability: Mold Breaker
EVs: 252 Atk, 252 Speed, 4 HP
- Dragon Dance
- Dragon Claw
- Low Kick
- Aqua Tail/ E-Quake (filler move)
No Outrage for the same reason as Flare Blitz; Outrage will confuse you & your Haxorus is liable to hurt itself (really badly even without a DD boost), shortening its life span. Dragon Claw is good STAB, Low Kick is coverage against Ice types, and Aqua Tail/ E-Quake are coverage moves of your choice.
Additionally, you'll be facing Benga @ the end (I assume, otherwise why go to Black Tower).
I would recommend a bulky water type as an addition to your team, like Samurott, Milotic, Azumarill, or Politoed, as they can also learn an Ice move as well. Weavile will also be of help, since it out speed both Dragons, has a very good attack stat plus STAB in super effective moves.
Weavile @ Expert Belt
Ability: Pressure
EVs: 252 Atk, 252 Speed, 4 HP
- Ice Shard
- Ice Punch
- Pursuit/ Low Kick
- Night Slash
Competitive set works just as well in-game; Weavile is frail, but it's there to sweep fast.
Milotic (fem) @ Leftovers
Ability: Marvel Scale
EVs: 252 HP, 252 Sp. Atk, 4 Sp. Def
- Scald/ Surf
- Ice Beam
- Dragon Pulse/ Attract
- Recover
I'd suggest Milotic over the others since it has very good bulk & a reliable recovery move.
Attract is actually not a totally worthless move in game, since you know what the main trainers' Pokemon's genders are. All of Benga's Pokemon are male, so if you want, you can use Attract. Dragon Pulse is there for coverage.
