I honestly have no idea why haxorus is so underused. Why does everyone say he's so bad? I think that he's one of the best lategame cleaners available right now.
People say that his speed sucks because he's outsped by hydreigon and latios. They can both hit him with draco meteor before he can do anything, so he sucks and should never be used. Do people look at him, think "rampardos" and move on???
Haxorus has 76/90/70 defenses, which are quite decent for something this fast and powerful. He has enough physical bulk to survive a weakish hit, and that's all he needs to set up.
His speed is, I think, really fucking good. He's faster than stuff like darmantian, kyurem and gliscor, and can outspeed the vast majority of the metagame after one dragon dance. With blazikens rear end fading into the distance, what can outspeed him? Hydreigon? Never runs timid, and sometimes not even max speed. Volcarona? Sure, but it could be bulky. Salamence? Eep!
Scarfers above base 95 speed seem to be disappearing. Genesect, hydreigon, landorus and garchomp are the only ones left from what I've seen. This means that haxorus has plenty of opportunities to sweep at +1.
His attack stat speaks for itself. It's the highest in OU. He's not rampardos or slaking either. He has that base 97 speed, manageable bulk, dragon typing and access to both dragon dance and swords dance. Hell, he even gets mold breaker of all things. Not truant or defeatist, Mold breaker. He can actually USE his attack stat without being hardwalled by four high OU pokes. He has no quad weakness like salamence does, he's neutral to mach punch unlike hydreigon, he has boosting moves unlike kyurem....
It seems like Haxorus has plenty going for him. He can break through anything not named skarmory, and looks badass doing it.
Also, why do people say that his movepool is shallow? He gets outrage, dragon claw, dual chop, dragon tail, earthquake, dragon dance, swords dance, taunt and a bunch of filler physical moves that are weaker than outrage when hitting SE. What else does he need? Fire punch? Aqua tail? Slack off? Extremespeed?
The dragon dancer is one of his best sets. DD/Outrage/EQ and Taunt/Dragon Tail/Dual Chop with Lum, draco plate or leftovers, jolly.
252 attack jolly has only one attack point less than adamant garchomp (393 - 394.)
Haxorus and rayquaza are the only dragons to receive both dragon dance and swords dance.
Haxorus learns outrage, dragon claw, dual chop, swords dance, dragon dance and taunt by level up. That's his entire competitive movepool bar earthquake and dragon tail, which he learns through TM.
His shiny colour is black. He shares this trait with rayquaza and dragonite.
His base stat total is 540, shared with kingdra, and the highest of all sub 600 BST dragons.
Only 5 fully evolved dragons have BSTs below 600, which makes haxorus 5th lowest. Below him is flygon (520,) altaria (490) and druddigon (485.)
Haxorus' prevo, Fraxure, could be usable in OU. It's stats are 66/117/70/40/50/67. His max attack is 366/549 (the same as jolly tyranitar) running adamant, (jolly is 333/499) and his max speed with is jolly 256/384 and adamant 233/349. His defenses are awful, but you can fix that with eviolite. He's gimmicky, but still better than druddigon. The catch? He can't learn earthquake! Brick break is off the list too, surprisingly, making dig his only option. Yuck.