Completing certain achievements in Legion Remix rewards some of the coolest sets WoW has ever seen.
Heroic Broken Isles World Quests IV requires players to complete 100 World Quest in Heroic World Tier as a Legion Timerunner. In this difficulty, mobs come with special affixes and are harder to defeat. This will provide you with the Ensemble: Sargerei Commander’s Voidscarred Regalia set.
For 
Mythic Legion Remix Raids, you must complete all Legion raids on Mythic difficulty. This includes Emerald Nightmare, Trial of Valor, The Nighthold, Tomb of Sargeras, and Antorus the Burning Throne. Rewards: Ensemble: Sargerei Commander’s Lightbound Regalia.
To Fel and Back – Completing the Legion Remix campaign rewards the Ensemble: Sargerei Commander’s Felscorned Regalia set!
Finally, completing any Timeworn Keystone Dungeon with a key level of 25 or greater with a Timerunner earns you 
Timeworn Keystone Hero and the Ensemble: Sargerei Commander’s Hellforged Regalia.
