Dark Ones (with swords) [20], Overlords [5], Snotspill
Harlequin Crest from Ogden upon returning to the shrine, a randomly determined magic item from Snotspill's remains, access to the fifth level of the dungeon
Ogden also initiates this quest when you talk to him after clearing a couple of levels in the dungeon. You'll know if you have this quest in your game because you won't be able to get down to level five until you solve it. The Tavern Sign is guarded inside a room by Overlords, and it will be the first time you meet these big guys. They aren't too difficult, especially if you have some spells (they have no immunities or resistances).
You won't be able to open the chest in their lair until you talk to Snotspill, a Fallen One leader who is on the other side of the room with the Overlords. He'll tell you to go get the sign for him. After you talk to him, if you haven't spoken to Ogden first to initiate the quest, return to town to do so now. Once back in the dungeon, go and get the sign from the lair of the Overlords. DO NOT give it to Snotspill. Instead return it to Ogden in town, and he'll give you the Harlequin Crest. Then go back into the dungeon and return to Snotspill, who will attack you immediately with lots of Dark Ones to help him. Firewall works wonders here. If you can't cast Firewall, wait outside the door and pick off Snotspill and his friends one at a time. Don't let them get through the door and surround you.
Dark Ones (with swords) [20], Overlords [5], Snotspill
Harlequin Crest from Ogden upon returning to the shrine, a randomly determined magic item from Snotspill's remains, access to the fifth level of the dungeon