@Ithilanor Well Priority Rain Dance Tornadus is certainly not a new thing, so yeah it could work. But we also need a spinner, so why not combine the two in Starmie if we decide to take that route?
Anyway I've just realized that no one has actually nominated a full Haxorus set yet, so I'm going to go ahead and do one for us.
@ Life Orb/Dragon Plate
Nature: Adamant / Jolly
Ability: Rivalry
EVs: 252 Atk / 220 Spe / 36 HP
- Outrage
- Earthquake
- Dragon Dance / Sword Dance
- Sword Dance / Substitute
Substitute would mainly be for maintaining the illusion, but can also act as a buffer against Priority after using SD or DD, allowing for extra kills. Also, blocks burns from the likes of Jellicent allowing for easier set up sometimes. SD and Dragon dance ensure that the opponent PAYS for a misprediction. It's one thing to screw up and lose a Pokemon, it's another to screw up and quite possibly have your entire team swept by a +2 Haxorus. After an SD even Skarmory is 2HKO'd with either item (though Rocks guarantee it with Draco Plate), meaning absolutely NOTHING can take the hit and live. Furthermore, they'll be scared to bring in their Skarmory or other steel right off the bat due to the threat of instantly losing it to Zoroark... and then REALLY being screwed. Dragon Dance is for against more offensive teams, Sword Dance for more stallish teams Haxorus outspeeds without the boost. Either way, shit is going to fall. I HIGHLY recommend this set because its offensive and illusionary synergy with Zoroark is insane. Of course exactly what combination of boosting moves and Substitute will have to be worked out through trial and error; I can't theorymon myself the best combination of the three well enough without testing.
Choice Band is also a possibility (I don't like Scarf as much because we really want that game ending threat there, which just isn't present with Scarf), but I like the idea that we can force a checkmate decision with just the threat of Zoroark combined with Haxorus with the boosting moves. Also, Choice band doesn't get a guaranteed 2HKO on Skarmory, and that shit is just too awesome to pass up.
Don't forget that this being Hyper Offense, there's no reason we can't run both Terrakion AND Haxorus on the same team. Between the two of them and Zoroark, the opponent will be hard pressed to not get swept.
Anyway I've just realized that no one has actually nominated a full Haxorus set yet, so I'm going to go ahead and do one for us.

Nature: Adamant / Jolly
Ability: Rivalry
EVs: 252 Atk / 220 Spe / 36 HP
- Outrage
- Earthquake
- Dragon Dance / Sword Dance
- Sword Dance / Substitute
Substitute would mainly be for maintaining the illusion, but can also act as a buffer against Priority after using SD or DD, allowing for extra kills. Also, blocks burns from the likes of Jellicent allowing for easier set up sometimes. SD and Dragon dance ensure that the opponent PAYS for a misprediction. It's one thing to screw up and lose a Pokemon, it's another to screw up and quite possibly have your entire team swept by a +2 Haxorus. After an SD even Skarmory is 2HKO'd with either item (though Rocks guarantee it with Draco Plate), meaning absolutely NOTHING can take the hit and live. Furthermore, they'll be scared to bring in their Skarmory or other steel right off the bat due to the threat of instantly losing it to Zoroark... and then REALLY being screwed. Dragon Dance is for against more offensive teams, Sword Dance for more stallish teams Haxorus outspeeds without the boost. Either way, shit is going to fall. I HIGHLY recommend this set because its offensive and illusionary synergy with Zoroark is insane. Of course exactly what combination of boosting moves and Substitute will have to be worked out through trial and error; I can't theorymon myself the best combination of the three well enough without testing.
Choice Band is also a possibility (I don't like Scarf as much because we really want that game ending threat there, which just isn't present with Scarf), but I like the idea that we can force a checkmate decision with just the threat of Zoroark combined with Haxorus with the boosting moves. Also, Choice band doesn't get a guaranteed 2HKO on Skarmory, and that shit is just too awesome to pass up.
Don't forget that this being Hyper Offense, there's no reason we can't run both Terrakion AND Haxorus on the same team. Between the two of them and Zoroark, the opponent will be hard pressed to not get swept.