Horror games are near and dear to my heart. I've been going through a zombies phase the last few years. Given my love of Risus combining the two is a no brainer if you'll excuse the pun. Which is where I run into a speed bump: how do you do Sanity checks in Risus?
The grandfather of horror games, Call of Cthulhu (Chaosium) introduced us to Sanity checks. Sanity became a finite resource. Exposure to horrors would gradually wear this down driving the character mad and has become a sort of standard feature of horror rpgs in one form or another.
The easiest way is to simply require a Sanity cliche. You could roll this cliche vs. a TN to avoid freezing in terror, screaming or running away etc. after a glimpse of the Great Old Ones. Faced by a minor monster the character might roll cliche vs. cliche in a single action contest. Losing could in effect rob him of his tools of the trade halving his cliches (you try finding that monster in your text of demonology when you're a few tacos short of a combination platter) for that encounter. Faced with the big ugly boss the characters might have to enter into social combat, Sanity cliches vs the monster's appropriate cliche, failure reducing them to gibbering minions or worse, winning meaning they can then try to enter physical combat with the eldritch being.
Introducing horror elements into an existing game is fun, but requiring a Sanity cliche might give the game away. It's also bad form to require such a cliche if you aren't using horror elements regularly. In this case you wing it with the available cliches. Keep in mind that checks vs. something commo charactern to a character will be about a 10, a firefighter (4) faced with a blaze won't even blink. Similarly the firefighter facing something horrific but related to a fire would be slightly higher, a burning body might be a 15. Something completely out of ordinary experience but related to similar events, like a burning body walking around setting fires might be a 20. Characters confronted with dangerous situations quite often in play might get a bonus. If our firefighter is on active duty and role plays fighting fires reasonably often he might need to roll a 5 or higher to ignore his fears.
Not al cliches are the same for facing fear. Faced with the same Zombie Horde (tm) an accountant, ex CIA operator, and Paranormal investigator might all act differently. In this case a GM could run a Fear vs. Sanity conflict with a separate Fear cliche for each character. The accountant faces Hordes of the Undead (4), the CIA spook faces Undead Hoaxers (2) due to his lack of belief in the undead, and the paranormal investigator faces Deadly Proof I'm Not a Nut (3.) His study of the occult and earlier investigations make him a little tougher than ordinary men and accountants but his belief in the undead also makes him more vulnerable than the spy who finds they are a trick.