Managed to grab a key and went with my Bowmaster friend.
1st stage: Kill a bunch of mobs, and then deal with the Whale Security Guard who loves to teleport you around the map. The map is more vertical than horizontal, so it's even more frustrating compared to the roleplay dungeon.
Oh, and you deal fixed damage on it.
2nd stage: Kill a bunch of mobs while dealing fixed damage. If your class matches the type of mobs, then you'll do 10x more (10 vs. 100). I recommend bringing one of each class to finish this stage quickly, or just bring 6 Phantoms and use Milles on everything.
The boss in this stage was kind of a pushover since we were able to keep it completely KB'd with Blaster and Soul Seeker.
3rd stage: Can't remember, but there were a lot of flying eels who died eventually (don't know why, I think it had to do with the runes scattered around the room) and a pushover boss with quite a bit of HP and some annoying Invincibility frames.
4th stage: More mobs (I think you deal regular damage) and a boss who only stays at the top level. I recommend bringing classes that can hit from the bottom platform (Bowmaster with Blaster and Angelic Buster with Soul Seeker dealt with this easily). Don't know what he's capable of since we stayed out of range for the whole fight.
5th stage: Princess No. We got her down to about 2/3rds but ran out of time.
At the beginning, she summoned some mobs who you can only deal fixed damage too (she did this twice). After that, she summoned eels and some more runes around the room.
I think she was healing at that point? Was kind of focused on trying to kill her, didn't really pay attention.