From the back of the "Face the Hydra" challenge deck, "This box contains sixty challenge cards and an instructional playmat. To play against this challenge deck, each player must have a Magic: The Gathering deck."
The challenge deck allows 1 person or multiple people working together to play against a programmed deck. The cards in this deck are not designed to be mixed with standard M:tG cards and have a distinct back. Players play their cards against this deck before running out of health. The challenge deck does not play cards normally. Each turn a card is drawn and its effect is applied immediately.