Played through this last night with my partner, and we had a great timel. Love the build-it-yourself card dungeon :)
I think this could easily be extended to multiplayer mode by just making the bosses a bit harder to vanquish - there's no clear instruction, so we figured bosses were meant to take 2 wounds to kill or vanquish since Dracua takes 3. For multiplayer, I'd just say the bosses take (number of players +1) wound to kill or vanquish and Dracula takes (number of players +2) wounds to drive off. We firgured 5 candles per person would be best as well, otherwise it's hard to keep track, sharing 'life-force'.