The author says Risus have mainly drawn inspiration from Ghostbusters RPG, but also GURPS, Fudge, Tunnels&Trolls and Over the Edge.
Your character is made with different Clichés, and you have 10 D6s to spread out between them. Clichés can be any concept you want; viking, chef, spaceman, poet, mage or all of these and a little more. Clichés are ranked from 1 to 6, and at character creation your highest Cliché can be 5.
Example: Blobnard the Barbarian Description: Tall, wide and gingerly jolly. He enjoys fights, food and and the occasional battle of wits on a chessboard. Clichés: Barbarian (5), Gourmet Chef (3), Chessmaster (2)
It is assumed that your character have all tools and powers associated with your Clichés, so the viking have his battleaxe and blond beard, the chef has his kitchen tools and chef hat, and the chess master would reasonably have access to a chessboard with pieces to challenge others.
You either roll your Cliché against a Target Number set by the GM ranging from (5, a routine for a pro) to (30, a actual superhuman difficulty) or an opposed roll against an npc or another player.
Combat is any kind of contest between opponents, for example: horse-racing, regular combat, chess match, banjo duel, courtroom antics. The GM decides what kind of Cliché is appropriate for a given contest.
The parties will use an appropriate Cliché for the given situation. If the character is seen to not have an appropriate enough Cliché, he might use half rating of a Cliché that's somewhat close.
Example: Blobnard will use Viking (5) in a fight Blobnard might use half Viking (3) for horse-racing, as it is a physical skill, but not really a Viking thing, where as a Cowboy would use whole his Cowboy Chiché.
Opponents rolls their Clichés as attacks against each other, and the lower roll loses the round. The loser of the round loses a dice from his Cliché for the reminding of the fight, and continues round for round until one side goes down to zero Cliché dice and loses. The contestants can use different Clichés if appropriate, but when the first Cliché goes to zero the character loses. The victor of the contest is free to narrate the results appropriate to the type cof contest and the GM can discard an inappropriate narrative.
There are extended rules for "pumping" your Cliché, using inappropriate Clichés, Lucky Shots, Teaming Up and Character advancement.