Unfortunately, I was clued into this late, and as of time of writing, it is Alterac Valley. The last puzzle is now bugged, and after all steps are completed and everyone’s quests are satisfied, it it does not let you end it. I did three successful tries (that is, completed all the steps correctly), twice clicking the hero power at the end as directed, and for the middle try I also tried clicking end turn. Nothing works, it always resets. Oh, well.