WoW Shadowlands Keystone Master for Season 2 is a Feat of Strength Achievement that can only be earned during the length of the Mythic+ Season 2.
WoW Shadowlands Keystone Master Season 2
Earning the achievement "Shadowlands Keystone Master: Season Two" grants the player the Soultwisted Deathwalker mount, a recolor of Shadowlands' Season One Keystone Master.
To earn the Season Two Keystone Master achievement, you must really dedicate yourself to Mythic+ as one of your main forms of content. You must earn a 2,000 Mythic+ Rating, over eight dungeons currently available for Mythic+, you would need an average of 250 score per dungeon.
Completing a +15 Keystone in time grants ~187 points. The fun part begins when you get the big points completing Tyrannical and Fortified +15 keys in time, granting you ~249 points.
Essentially, you must complete every dungeon +15 Tyrannical and Fortified and you will just squeeze into that 2,000 required Mythic+ Rating to earn the achievement.
This is a controversial move from Blizzard, as every previous Mythic+ Season only required the standard +15 on every dungeon, still a challenge, but very doable with even just a solid M+ spec, and great knowledge of the dungeon. Now, you MUST complete and time +15 Tyrannical and Fortified on all eight dungeons, a tough feat indeed.