trial of the magians finale.....
Any dagger trial, including relic/mythic/empyrean/other magian dagger. Trade 10x Thief Knife. Final result, Treasure hunter +1. The only caveat would be that if the dagger already has magian trials, all magian trials must be completed. Repeatable, I don't think +2 TH on weapons would be game breaking at this point.
Could even make it a two part trial, 10x for +1 TH, 100x for +2.
This kind of trial isn't even without precedent. See Arka IV.