Card battles
You can unlock the card minigame by checking out the wall of originals or visiting the Game Place. Once unlocked, Chris can challenge any NPC to a game (be they real or not), but don't expect everyone to accept.
You'll want to challenge as many characters as possible if you want to complete the various card sets in the game.
Why? Because Chris will gain a permanent increase to his mood bar (the mana/magic meter of the game) the bigger your collection gets. The more cards you collect, the happier Chris will be, and you'll be able to perform more moves during the fights against those dang, dirty trolls.