I would say that Haxorus is going to take the biggest drop in usage, but I don't see it going into UU. Garchomp can do most of what Haxorus can, as well as being much faster than it. Haxorus still has Superpower and a higher base Attack stat, which may be able to save it from falling into UU. Although if any dragon were to fall in usage heavily, and possibly into UU/BL, I would put my money on Haxorus being that dragon.
Haxorus existed in a metagame where chomp was legal you know, just sayin' (which ironically, this was when Haxorus was highest in usage). If anything is going to cut into its usage, it's Genesect, and even then you can still feasibly use Haxorus with the existence of Genesect in BW2. If you want to use Haxorus in BW2 though, you're going to have to make a concerted effort to accommodate it on your team, because otherwise you're better using Garchomp since it's "easier, better on average AND IT AVOIDS THE OHKO FROM +2 MACH PUNCH WHAT NO FAIR :<." Haxorus still has its tiny niche in over Garchomp with Choice Band but really, the sets worth mentioning are the Sword Dance sets.
SD Rain Abuser Swords
SD Fight gem
Haxorus (M) @ Fighting Gem
Trait: Mold Breaker
Shiny: Yes
EVs: 36 HP / 252 Atk / 220 Spd
Adamant Nature
- Swords Dance
- Outrage
- Superpower
- Substitute / Earthquake
&&
SD Yache
Haxorus (M) @ Yache Berry
Trait: Mold Breaker
Shiny: Yes
EVs: 200 Atk / 88 SpD / 220 Spd
Adamant Nature
IVs: 11 Def
- Swords Dance
- Outrage
- Taunt / Aqua Tail / Earthquake
- Low Kick
&&
Haxorus (M) @ Lum Berry | Aqua Plate
Trait: Mold Breaker
Shiny: Yes
EVs: 36 HP / 252 Atk / 220 Spd
Adamant Nature
- Swords Dance
- Outrage
- Aqua Tail
- Low kick
The 1st SD set is the strongest one it can run in OU. It kind of plays like Double Dance by subbing or SDing depending on the situation and going from there. At +2 you are pretty beating every single wall in the game, including Skarmory (Superpower doles out: 271-319 81.13 - 95.5%and OHKOes SpD Skarmory,)The Choice between EQ and Substitute is a tough one, but ask yourself this: Does Jirachi fuck me? Should I not waste my fight gem on jirachi? If your answer is yes to either of these questions, go with EQ otherwise stick with Substitute since it's better against offensive teams. My favorite part about this set is OHKOing Genesect with 0+ Fight Gem Superpower, though only an idiot would do that. Right? Right???
The 2nd set is pretty decent against most teams, but has less of a payout if that makes any sense. Yache Berry Haxorus gets the jump on most Genesect since the natural impulse is to Ice Beam, which does like 40% to this set because it doesn't get a SpA boost. It's cool to avoid the OHKO from HP Thundurus-T, Starmie or getting slamed by Mamoswines Ice SHard. It's weaker than the 1st & 3rd set, but it's probably the most "consistent" one. Taunt let's you beat Skarmory (though you'll get crippled in the process) Aqua Tail invariably sees use on Rain Dance teams and Earthquake just smashes Jirachi. The drop in physical defense seems like a big deal, but its not. Haxorus is shockingly frail.
The 3rd set SD is predictable rain abuser, thought it was at its strongest when people were still attempting to use stall. It's still good; good against sun & balanced teams that utilize Skarmory, but kind of dead weight against heavy offense teams.
TL;DR
HAXORUS!
AWESOME!
THAT'S REALLY ALL THERE IS TO SAY ON THE MATTER
PS: For the love of god, don't use Dragon Dance tUmUt
PS2: Yes, the shiny trait is mandatory