Haxorus is currently hard-walled by Steels. It needs Earthquake to even get past them.:
-Dragon Dance/Swords Dance
-Outrage/Dragon Claw
-Earthquake
-Poison Jab/Swords Dance
Nature: Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Lum Berry/Life Orb
Ability: Mold Breaker
However, Haxorus isn't as good as it used to be because 97 Speed is kinda awkward. Just putting that out there.
Mega Altaria can go two different ways with Dragon Dance: bulky or offensive. Its Mega Stone is one of the easiest to obtain in OR/AS; you just have to show your Altaria to a Collector hanging outside the Pokemon Contest Fan Club:
Bulky (can afford to set up more than once or twice before going for a sweep):
-Dragon Dance
-Return
-Earthquake/Heal Bell/Substitute
-Roost
Nature: Impish
EVs: 248 HP/136 Def/96 SDef/28 Spe
Item: Altarianite
Ability: Natural Cure
Offensive:
-Dragon Dance
-Return
-Earthquake
-Roost/Fire Blast
Nature: Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Altarianite
Ability: Natural Cure
Thank you. I was unaware about some of those things
since you say haxorus isn't the best choice, what would you recommend? is there something I can get in OR that would be better?
I also have another question you might be able to answer. I recently learned how to ev train, but when I use a recommended set they dont add up to 510, they add up to 508. so when im done it doesnt say its a fully trained pokemon. does that matter?