Manastorm Mystique

There are invisible walls preventing you from exiting through the doors, but you can run up the stairs and get out of the inn through the balcony. It's just plain old Northrend Dalaran out there, complete and populated, albeit minimally, by levelers. You keep the Time-Displaced Veil buff while in town, but lose it if you leave (fortunately it comes back when you return so you don't have to take the long way back).

The quest doesn't specify, but this is a special instance of Dalaran. Use the portal that's in the Everywhere Inn (where you picked up the quest), don't use your Dalaran hearthstone.

I chose the Tell her a joke option.
Millhouse Manastorm says: Ok Millhouse, You got this. Your best joke. Here we go.
Millhouse Manastorm says: Excuse me.
Millhouse Manastorm says: What do you call Rhonin when he's been polymorphed into a pig?
Millhouse Manastorm says: The Archmage of Dalaham!
Millhouse Manastorm says: You see, because...
Millificent says: That was a terrible joke. Possibly one of the worst I have ever heard.
Millhouse Manastorm says: Oh...
Millificent says: I love bad jokes! Okay funny man. Tell me another.

Completed the quest successfully.