This hack isn't a dead-on probability simulation of the dice method in Mouse Guard, but if you have a deck of cards and no dice, it'll work.
- Use the full deck of cards, with ONE joker included.
- Draw a number of cards equal to the number of dice that would normally be rolled in a given situation. Helping players draw from their own deck, if they have one.
- Red suit cards and the Joker count as a success. Black suits count as a failure.
- Any Red Jacks, Red Aces, and the Joker can be 'exploded', as per the rules for Persona points and sixes in the basic rules.
- To tweak up the chance of success and the chance for "explosion" slightly in the players favor, add the second Joker back in.
- Reshuffle the deck after each Test. For Conflicts, don't return cards to or reshuffle the deck until the full Conflict is over.