Dragonflight Season 3 Master is returning in Patch 10.2 awarding players with 1 Heroic Tier Set piece.
To earn the achievement, you must complete one of the following during Season 3:
Clear Amirdrassil on Heroic Difficulty (Heroic: Amirdrassil, the Dream’s Hope);
Earn the Challenger II Rank in Season 3 (Challenger II: Dragonflight Season 3);
Earn Dragonflight Keystone Master in Season 3 (Dragonflight Keystone Master: Season Three).
Once you earn any of the 3 achievements above, you will receive 1 Emerald Mark of Mastery that you can turn in for 1 Heroic Tier Set piece.