What is the quickest way to unlock the Rose Knight?
The quickest way to unlock that hero is to rush your kingdom to level 17. Then build a team composition to counter that 6-12 elite boss. It's highly recommended that your team consists of 2 stunners, one tank, one damage dealer, and one healer. I also suggest that your heroes are at least level 50 before attempting the dungeon. Levels do matter! The team that I used had Prima Donna, Death Knight, Child of Light, Black Crow, and Tracker.