A showdown is a special combat situation in which two (usually) armed combatants face off at relatively short range (within the same zone) in a deadly contest of speed and marksmanship. Since this is such an integral part of Wild West mythology, it deserves some unique rules.
There are three phases to the showdown: Staredown, Draw, and Fire.
The Staredown is a contest of Resolve vs. Resolve. The gunslingers stare each other in the eye mere seconds before facing death itself, simultaneously daring the other to reach first and trying to shatter his nerve. Mechanically speaking, although it involves intimidation, it's a little more about not breaking than it is about striking the fear of God into your opponent, so we'll use Resolve (it could arguably be called a use of Empathy, as well, but Resolve seems much more Wild West than Empathy). Whoever loses the Staredown is the first to "reach," and the winner gets to declare an appropriate, fragile Aspect on his opponent, like "Shaken," that can be tagged for free in the next phase or tagged with a Fate Point in the Fire phase.
Draw is when the gunslingers actually reach for their weapons. Generally speaking, whoever reaches first is seen as either less honorable or more cowardly (these are often synonymous), whereas the gunslinger who reacts to the other's reach is considered braver and more skilled, since he reaches after his opponent but has to get a shot off more quickly to survive. Draw is a contest of Alertness vs. Alertness. Either gunslinger can make a "hip-shot," and receive a +1 bonus in the Draw phase in exchange for taking a -1 penalty in the Fire phase. A character with the Lightning Hands Stunt may use Guns instead of Alertness in this phase; a character with Quick Draw ignores the -1 penalty in the Fire phase when making a hip-shot. Whoever wins the Draw phase acts first in the Fire phase.
Fire is the moment when pistols are pointed and triggers pulled, and uses the Guns skill. Whoever wins the Draw phase gets to Fire first and potentially (hopefully) take out his opponent before he has a chance to retaliate (the Snap Shot stunt can be used in this phase to pre-empt the initiative order established in the Draw phase). Since each gunslinger is standing still and not attempting to dodge, neither can use Athletics (or any skill) defensively -- or, if he does, he forfeits the chance to Fire and is immediately seen as a coward by any witnesses. Damage resistance doesn't seem to be a factor in the source material, so defending with Endurance doesn't seem appropriate, either. Indeed, the only challenge seems to be to shoot the other guy before you get shot, and since everyone's an equally hittable target standing still, everyone should face a static difficulty number -- say, Good (+3). Obviously, that's not going to be too tough to beat, especially for a character with Superb (+5) Guns, so the fight is often won or lost in the Draw phase. Unless the first to fire scores a Moderate or better Consequence, the other gunfighter may also take a shot.
- Alternative Idea: The participants could defend with their Resolve rolls from the Staredown phase. The truly fearless and resolute seem to be harder to hit in Wild West showdowns in the movies. The downside to this is that it'd be much, much harder to, say, kill a guy. A Resolve roll is likely going to total more than +3. Then again, it's some additional bookkeeping (i.e., you have to keep track of what that Resolve roll was), so that may be a turn-off.
If the results turn out to be non-lethal, whoever inflicts the higher Consequence is "the winner," although it's important to note that "winning" a showdown is no guarantee of survival. A Severe Consequence, like "Bleeding To Death," ought to do the trick by anyone's standards. If either participant chooses to continue the conflict, normal combat rules apply.
(It should be noted that there are some other changes to Stunts in "SotW," like deleting On Top Of It and Snap Shot, that address some potential problems here.)
And one of my favorite "SotW" Stunts:
You Know Where the Next One's Goin' [Prerequisite: Gunslinger]: Spend a Fate Point to deal Composure Stress instead of Health Stress with your Guns skill. Outside of a showdown, your opponent defends with Resolve; in a showdown, the static difficulty is equal to your opponent's Resolve.