Returning from Dragonflight, the Mark of the Spelunker Supreme is awarded for defeating Queen Ansurek on Heroic difficulty, reaching 1600 Rated PvP ranking, or 2000 Mythic+ rating, and can be turned in for a single free piece of Heroic-level tier gear!
The mark can be redeemed from Ab'xal or Ip'xal in Azj-Kahet's City of Threads.
Following the trend set in Patch 10.1 to help players acquire tier set bonuses more quickly, The War Within Season 1: Spelunker Supreme gives players three avenues to receive the Mark of the Spelunker Supreme, combining nicely with the Revival Catalyst. Between the two, players can quickly complete at least their two set bonus, regardless of how lucky they are with loot drops.
The first Revival Catalyst charge becomes available with the start of Season 1 on September 10th, followed by another charge every other week after.
The first Season release schedule for The War Within is a bit of a special case though.
Because Mythic+ is not available until September 17th, this means the Mark is only obtainable through PvP or defeating Queen Ansurek on Heroic difficulty though — something that may not necessarily be within everyone's grasp on week one. As the final boss of Nerub-ar Palace was not tested on any difficulty, it's hard to say what the difficulty curve will be, though historically the final boss on Heroic is typically on par or even harder than entry Mythic raid bosses.
Whatever the case, players who are not clearing the Heroic raid will still be able to start accumulating Mythic+ rating once Mythic raid difficulty becomes available the following week on September 17th.