Corresponding with someone thinking of running a single session game got me thinking about what works best in that format, and I took the time to get all my thoughts down.
Now, I have to admit that I haven't run many one-shots with the rules in their current format (although plenty before it was an Apocalypse World hack). So this is a little experimental, and I'll be very keen to hear how the guidelines go in play.
Here they are:
Monster of the Week as a One-Shot
If you want to run a single mystery maybe as a convention game or for something different from your usual game, here's some stuff to do, or at least consider.
First, the hunters should not have all seven luck points available. Instead give them from one to three (depending on how tough you want it to be). You might allow everyone to take a free advance when they create the character, to make them a little more awesome.
It's useful to pick a frame and just tell everyone who the team are and how they operate. You may want to emphasize certain characters, or make them mandatory, and de-emphasize or leave out others. For example, if you go for a frame centered on the Professional, having an Initiate in the team might not work easily.
I strongly advise letting everyone make up their own hunter (even if you restrict the types available). Customizing your hunter is a critical bit of ownership for the players, so resist the urge to save time by doing that for them. Pay close attention to all the class-specific moves each hunter has, so you can give them a chance to use everything.
In general, follow the instructions for a first session. Go a little easier on the questions, as you don't need to build a mythology from the answers. You might also spice up the mystery a bit more than usual for a first session, too. A twist or two works very well in a one-shot game. You should be prepared to maybe switch some things around to fit with how the hunters come out, or even quickly sketch the mystery as they make up their hunters rather than prepping it beforehand.
Even if you skip the full-fledged prep beforehand, you can make things easy on yourself if you bring a map or three of possible locations, a list of names and maybe even some pre-written bystander threats (it's a rare mystery that can't fit a suspicious cop or some naïve victims).
Without the expectation that the game will continue, you should also feel free to ramp up the dangerous threats and push for more horror.
Also, think about the scale of events. There's no reason not to let the stakes of the mystery be huge: zombie epidemics, the legions of Hell being unleashed on earth, hideous gods from beyond the stars and other enormous threats are all fair game.
If your team includes hunters with central story elements (the Chosen and her destiny, the Wronged and his nemesis, the Professional and her Agency, the Initiate and his Sect, etc) then tie those into the mystery as well.