Haxorus is considered unviable in SV OU (no ranking in VR). It has a bad offensive typing, and is easy to revenge kill due to its poor bulk, difficult speed tier, and lack of priority. (First Impression doesn't count as it's an anti-synergy with Swords Dance and means you get walled by Steel)
Furthermore, Haxorus directly competes with Dragonite, which is a top-tier threat with a better movepool and matchup flexibility. The one thing Haxorus does better is stallbreaking, due to Mold Breaker ignoring Unaware. The archetype most interested in that skill set is hyper offence (HO), which also helps Haxorus by not having to pick up for it defensively.
Screens: This is a common HO archetype that will suit Haxorus well, as it helps you get boosts. Deoxys-Speed, Zamazenta and Ninetales-Alola are the main setters. Sticky Web via Ribombee is another possible angle that decreases the pressure to get speed boosts from Scale Shot.
Typical HO teammates: If you're building HO, then the usual suspects like Iron Moth, Ceruledge, Kingambit etc are likely to help. They match well into offence incl Gholdengo, which is important because Haxorus is bad against those things.
Way to chip Corviknight and Skarmory: These two are common on fat teams, and they beat Haxorus 1v1 with Roost + Rocky Helmet or Whirlwind. Haxorus only has a chance if they're chipped a lot, with +2 Close Combat 2HKOing both of them (mind Close Combat's low PP though, especially against Pressure Corviknight). Stealth Rock helps you force that damage, so Great Tusk would be helpful, or maybe you could try a Glimmora team. Attackers that encourage Corviknight to switch in rather than Dondozo would also help. Ogerpon-Wellspring, Rillaboom and even Dragonite itself have this quality. Obviously, Fire and Electric types beat them too, but remember stall players will just swap to Blissey.
Priority: Haxorus is horribly slow against every offence team, so speed control is urgently required. Dragonite, Kingambit and Ceruledge are the main options that make sense on HO. Some more niche users include Scizor, Weavile and Rillaboom.
Knock Off: Gets rid of Heavy-Duty Boots and Rocky Helmet, which is very helpful to physical breakers like Haxorus. It's a bit tricky to fit on HO, but Ogerpon (all forms), Iron Valiant, Weavile and Scizor provide options.
Hazard protection: If your team relies on Stealth Rock or Sticky Web, then Air Balloon Gholdengo (to stop Defog and Rapid Spin incl Great Tusk) will be hard to pass up.
