Am I a man or am I a muppet? If I'm a muppet then I'm a very manly muppet!
We shuffle the merchants and randomly pick one -- the original merchant gives less selection but halves the price of 2 items. The new merchant gives a bigger variety but everything is full price. If an item comes out that's class-specific to a class not being played, we discard it and redraw.
That's a good idea... I just pull out all the class-specific cards based on which heroes are in the game.
We are currently playing with the original room cards as after a few games we haven't quite seen every critter in the base game, but soon we'll shuffle all the room cards together.
Right now, we're playing with both decks shuffled together (as well as shuffling in the Dark Passageway cards)... but I'm curious what the "official" ruling is supposed to be.