After defeating Seriende, search and reveal a hidden north. Go north and attack the mimnosuffogator then wait in the room, after a while a Archmage of Tame will walk in and grant the mark, or you will be teleported to the beginning of the Catacombs of Shame.
For experiencing a sudden moment of realization, the Powers granted thee a Mark. You have been granted The Mark of Epiphany! You gain 15 practices!