The GM can keep a stack of creature cards and use them as a wandering monster table. Or at least use the cards when the players deal with creatures. General abilities (flanking, phasing, flying, etc) or special ones as described on the card should be translated to the roleplaying situation as much as possible.
Creatures are much stronger than in Magic. A 3/3 creature can be quite deadly, as a character or group of characters can only kill it by doing three points of damage in one round. Except for experienced warriors (with a high combat skill and a lot of red pips in their deck) many people will have difficulty overcoming them.