More to the point, I think it could be awesome. There are a lot of peculiarities to the Fate system that, if calibrated appropriately, should be able to produce a meaty, flavorful kind of brutality that would fit the Call of Cthulhu mind set better than the very oldschool BRP system.
Puny mortalsFirst and most obviously, the PC power level should be lower than the SotC standard. I'd go with "Good" quality PCs, meaning they'd each get a skill pyramid capped at the Good level (+3) and just 6 aspects.
I think I'd also scrap stunts completely, since that would further lower the PCs' power level and save a hell of a lot of time in character generation (which, after all, needs to be quick in a high-lethality horror game), but the upcoming Dresden Files RPG might include genre-appropriate stunts that'll change my mind. Anyway, if stunts are out, then I'd use some variation on the stuntless SotC variant rules to give aspects a bit more utility.
Another severe change I'm leaning towards would be to limit the fate point refresh to half the number of aspects, so PCs would start each session with only 3. Limiting players' narrative power is crucial to the genre, and it would also increase the importance of compels (and, therefore, encourage players to make more flawed characters than usual). However, I'd take some of the sting out this fate drought by letting PCs spend a "virtual" fate point if, in the course of the same action, they also take a consequence. That is, they have the option to take some physical or psychological sacrifice in order to give themselves better chances at success. After all, sacrifices (as a theme) and consequences (as a mechanic) are pure gold for horror games. More on that below.
A terrible price...In fact, I'd say that consequences are so important that I'd remove stress tracks from Fate combat system all together. Yep, any shifts of damage inflicted on characters would either be converted into consequences or take them out of the fight (a variant originated, as far as I'm aware, by Colin Jessup for his Star Wars Fate hack).
Now, in order to make room for all these consequences the poor, brutalized characters will be collecting, I'd let physical and psychological consequences use separate slots, and extend the spectrum of potential survival harm one more level, as below:
- Minor consequence - Covers up to 2 shifts of damage. Goes away as soon as the character gets a few minutes' respite. Things like "bruised", "winded", and "shaken" would be appropriate.
- Major consequence - Covers up to 4 shifts of damage. Lasts until the character can get a serious rest--like a night's sleep--or some specific remedy is obtained. A physical major consequence like "bleeding" might be remedied by medical treatment, while an emotional one like "infuriated" or "humiliated" might require something like an apology from the party who inflicted the consequence. I think any remedy that doesn't require several hours of time ought to require some kind of skill check or story-based accomplishment.
- Severe consequence - Covers up to 6 shifts of damage. These would, by default, last until the character has a chance to get days or even weeks of downtime, but might be reducible to major consequences by some kind of skilled treatment. Broken bones and real mental trauma would fit this category. Also, I might deviate from the SotC rules a little bit by saying that a character who takes a severe consequence is taken out, just not permanently, and not on the attacker's terms. So, in that way, it would work a little like a concession.
- Extreme consequence - Covers up to 8 shifts of damage. This would cover permanent harm, things like lost limbs and lasting mental afflictions. Naturally, taking an extreme consequence would definitely include being taken out of the conflict, as above. And, what's more, it might mean the permanent loss of the character--to death, madness, or what have you--if they can't get help afterwards: If all the PCs are lying around in pieces with no one functional enough to so much as provide first aid, that's a total party kill. With time and treatment, however, extreme consequences become regular permanent aspects. (Clearing that extreme consequence slot for more hurt, of course. Just because your character's already lost an arm doesn't mean he can't lose an eye once he's back in action.)
I'm a little bit torn as to whether or not the Endurance and Resolve skills should give characters in this system more consequence slots the way they give SotC characters more stress boxes. On one hand, I'd hate to devalue those skills, and the strategic question of whether to take a 4-shift hit as two minor consequences or one major one sounds like fun. On the other hand, I'm afraid it might make them--especially Resolve--too important. After all, Resolve is already rolled as an active defense against emotional and psychological attacks . . . and that's something a horror game should include a lot of.
Speaking of which...
A fate worse than deathArguably, the defining element of the Call of Cthulhu gaming experience is the sanity check. Any system trying to emulate this genre absolutely needs to include something along those lines. And, believe it or not, I think Fate already has a system which can that kind of thing beautifully: our good friend "consequences". Just let sanity-threatening situations make a psychological "attack" on characters (which would naturally be resisted with a Resolve check). Any consequences a character suffers as a result of such an attack could be states of fear or nausea or confusion, or the kind of colorful temporary (and sometimes permanent!) insanities familiar from good old Call of Cthulhu.
And, of course, because the "death spiral" effect is also important, new shocks would get to tag the consequences inflicted by previous shocks. That is, if you're already shaken by the corpse you found in the street, you're all that much more likely to lose it completely when the thing gets up and lurches towards you.
I'm not entirely certain, however, if sanity threats should actually roll to attack, or if they should just have a static horror factor that characters have to roll against. I suppose it's a question of just how much randomness feels right in play (and how much dice-rolling you want to do).
I'm toying with the idea of letting very successful sanity checks create temporary aspects along the lines of "keeping cool", "ready for a little blood", or "facing the darkness". Like a kind of anti-consequences, these would show that the character is hardened or inured to certain shocks, and would be invokable for a Resolve check reroll or bonus when a similar situation comes up. They could even mirror consequences in their values and time limits. That is, getting 4 shifts on a successful sanity check would create a major anti-consequence (for lack of a better term) that would last the rest of the day. I could complicate matters further by having these things actually take up psychological consequence slots--so that they'd make you more likely to break more severely once something does manage to crack your defenses--but I fear they'd become a punishment for rolling well rather than a reward. Not too sure.
A desperate struggleOther than the elimination of stress boxes, I'm only envisioning rather minor changes to the combat system.
Naturally, I'd have weapons grant bonus shifts of damage on a successful hit, as a whole lot of Fate mods do. I don't think I'd bother introducing any sort of armor rules (beyond the possibility for characters to invoke aspects like "bullet proof vest" or "squamous hide" on their defense rolls).
I'd like to replace Fists, Weapons, and Guns with simple Melee and Ranged skills. Melee might continue to be a defense skill--but only against melee attacks--while Ranged might only be for attacking, and dodging ranged attacks might only be done with Athletics. I worry this could be a bit too harsh, though, since PCs in this variant would have far fewer skills than SotC PCs.
I haven't really done any thinking about magic rules. There are a whole lot of Fate variants addressing that issue already, and even one specifically aimed at Call of Cthulhu-style magic, and I'm not sure it's really high priority to begin with.
At any rate, I don't expect to have a use for any of this system-noodling any time soon, but it'll be worth looking at again when I've got a copy of Starblazer Adventures or Dresden Files in my hands.