Many games have attacks with continuing effects. The most popular example is probably fire. Hit a target with enough flames and it catches fire itself and burns merrily. There are other examples of course: poison, acid, smear campaign, a magical curse and drowning to name just a few. How do you represent this?
First of all combat in Risus does not necessarily mean being shot up or stabbed. It can be a matter of losing position or will to fight or just being placed in a spot where you have to surrender or die. So some of these effects are more appropriate for lethal combat. Again, there are no hard and fast rules in Risus. Setting a mage's robes on fire will certainly crimp his spell casting. So here are some thoughts on how to model continued damage.
Poison weapons: poison can be a bonus to your die roll or an extra die. You could also give an assassin type character a double pump cliche like Poison Master . He's capable of a brutal attack or two them must reload his potions and venom up his blade. If any characters want to use his wares without the appropriate cliche then remember that accidents happen. Another way to model poison could be a single exploding die added to your attacks for special gear. You have a certain number of doses of poison and then that is used up buy another bottle.
Longer lasting poisons could have a cliche themselves Lethal Blade Venom (3) that keeps attacking your character in a fight as he faces more mortal opponents. Less lethal poisons might only count sixes rolled and in effect be part of a team (working on the inside.)
In keeping with Risus I'm not going to give elaborate damage tables for different attacks. Most continuing attacks will take one of the forms given for poison.
In social combat smear campaigns or a scandal might give continuing damage that hampers a character's negotiations or court case. A magical curse might take the form of a cliche the character must combat; a vampire sets his Iron Will (4) against his Unholy Nature (Burning in daylight, being repelled by holy symbols, bloodthirsty) (5) to avoid draining his love and then later must fight his enemies in sunlight where the Unholy Nature becomes a member of the Vampire Hunter team. As he fights his foes, he burns. At high noon the Unholy Nature might be a second separate attacker.