I am the Warden!!
In the Optional System, a stunt is an attempt at completing two options simultaneously. Seems fairly simple, right? Yet no other concept in the game has undergone so many revisions and tweaks or caused so many bald spots on my precious scalp. As the game evolved into a more complex ruleset, stunts became a liability and was nearly cut from the entire process.
Many other games use a stunt mechanic, but these are your typical point distribution. Do this real good and you get a stunt point, or everyone gets to do one stunt per encounter, blah, blah, blah. Not me. I always wanted stunts to be an integral part of the game with inherent risks and wicked benefits, it just never played out quite as I hoped at the table.
Over the past couple of weeks as the latest batch of revisions make it from brain to computer, it's the stunt mechanic which has undergone the largest transformation to what I believe (AKA hope) will be the final version (or final enough that it just needs a little tweaking with difficulty dice and such).