I introduced the deck as the party, then 11th-12th level, was finishing a plot arc that had lasted about four sessions. First draw: mage's soul disappears. Getting it back required a trip to Sigil lasting 4-5 more sessions. Everyone had a good time, though. I brought in the deck because I'd never had the chance to draw from one as a player, and also because one of my players likes to gamble and I knew he'd want to draw.
