US Marshals uses an original game system from Fat Goblin Games, The Difference Engine. All challenges in the game boil down to a simple mechanic known as The Difference Engine; two opposing rolls of a pair of six-sided dice (2d6), each with a modest Bonus added. You compare the results, calculate "The Difference," and use that to determine success directly — the greater The Difference, the greater the effect! In something like combat, that may mean The Difference is added to a weapon's damage, while if attempting something like a long jump across a ravine, The Difference could equal the number of yards your character can make it with a flying leap. Dynamic difficulties that change with each roll of the die and built-in variable success help to inform the narrative with each challenge in The Difference Engine, moving the story forward in exciting ways from moment to moment.

All you need to play are these rules, a few scraps of paper, pencils, at least two six-sided dice (2d6), and a few friends! One person runs the game as the Gamemaster (GM), while everyone else plays as a Marshal; the more the merrier!