We already saw a sort of "opposite" Blair in Evan Hanley... instead of a confident, masterful right-hand man of Satan himself, Evan was a cowardly pompous wanna-be... and was hysterical because of it.
Penny... I want to fully explore your potential theological quagmire. A Good PT Devil? What about the Man Upstairs?! There's a world of trouble for us to get into here, and so little time.....
I'd have loved to see our Barnabas try the old "I'm a cousin from the English branch" routine, only to have their Barnabas step in from off-camera.... but be fair, how much of a fraud can they think he is, when he looks EXACTLY like the other one, and the portrait?
I've also had the desire to see too much time travel on DS, to the point where BC shows up in 1980 and tries the bit again, only to be told, yes, you live in the Old House already, idiot!