Publisher's Description (from website)
'Tis the season to be munch-y! In this, the season of giving and receiving, we invite you to give monsters some pain and receive all their stuff. Or, if you want to be marginally nicer, you could give them this official Munchkin holiday greeting card, complete with a new rule for the game!
And then kill them and take their stuff.
Merry Munchkin Holiday Card Rule
Once per game, if you have a Merry Munchkin Holiday Card on the table, you may draw one face-up treasure as a gift from Steve Jackson Games. You may do this at any time, even during combat. Limit one Holiday Card per player.