Tier 20 is the armor set associated with the Patch 7.2.0 and is obtained from Tomb of Sargeras.
Each set consists of six pieces and has four ranks: Raid Finder (890+), Normal (905+), Heroic (920+) and Mythic (935+).
This set is the second one after T6 to have more components than the standard 5-piece tier. This change has been made to fit two legendaries that may could share the same armor slot as tier pieces.
The Tier 20 items and tokens drop from raid bosses in Tomb of Sargeras.