Sitting here, staring off into space (brain locked)

[Tinner]

The bedroom of a duke taken over by an Angel of Decay?
Sounds like an excuse for depravity to me!

Does this need to be a fight encounter?
You could add some pretty Eric's Grandma unfriendly stuff to this room that wouldn't necessarily be a fight, but would still make the room memorable.

Angel of Decay puts me in mind of some very, very sick bed-partners for the duke ...

 

[Mystery Man]

Wha haha...

What if the last chamber isn't a chamber at all, but a portal to an ALTERNATE plane where the castle is upside down? To find the REAL villain, they would have to progress through an alternate, harder version of the castle and find their way back OUT.

I saw this in a video game before, and I REALLY enjoyed the concept.

Actually that's not a bad idea. But, I have something like this coming up for a future encounter. Once they realize (if they realize) who's pulling the strings they'll have to find a door to a lair of the mastermind (haven't got that far yet, don't know who or what probably a powerful lich) in this plane. Getting to him on the plain where his lair really resides is easy. Except its on the other side of the Sharn Wall, (the FR Phaerim prison) and trying to get in from that side will be suicide. Knowing them they'll probably try...