With the release of the Creation Catalyst, players can turn Sepulcher of the First Ones BoEs into Tier Sets. This allows players to get Mythic Tier pieces if they have Mythic raid BoEs! Players are able to buy BoEs of the Auction House or get them to drop from raid. If you have a Mythic BoE on Helm, Chest, Gloves, Pants or Shoulders, you'll get a 278 Tier Set Piece — equivalent to base Mythic item level. This is great for characters which could use an item level bump, including alts! These are the BoEs that each armor type has that will turn into a Tier Set piece.Cloth
Hands: Vandalized Ephemera Mitts Shoulders: Devouring Pellicle ShoulderpadsLeather
Helm: Hood of Empty Eternities Pants: Subversive Lord's LeggingsPlate
Hands Gauntlets of the End Shoulders: Pauldrons of Possible Afterlives Read more on wowhead.com