All expansion packs include optional characters that can be played in any combination (unless specified). You can use as many as you need and they will have the same game materials as the rest of the players. They'll never know they were optional to the game!
Please note: all expansion packs are linked to the main game page so if you don't want to hunt below for your game &/or if you want to be certain you are selecting the appropriate expansion pack, go to the 'helpful links' section.
These are the instant download versions of the expansion packs - available immediately upon purchase. If you need to have characters added to your existing party ready pack as an add on, you'll need to add party ready pack players.