Jeremy D. recently posted this simple and elegant stunt system based on the DCC deed die but intended for use with traditional rules. The basic idea is that attack rolls are made with d16 + class hit die (assuming B/X style variable hit dice), and a pre-declared stunt is successful if the hit die comes up 4 or greater and the attack roll is high enough to hit. This gives fighters (d8 hit die) roughly a 62% (4 or higher on a d8) chance of pulling off a stunt, given a high enough modified attack roll. Magic-users (d4 hit die) have a 25% chance (4 or higher on a d4). What’s the trade-off? If the stunt fails, the attack misses, even if the number would have been high enough to hit had a stunt not been attempted.
The system is clean, but does require Zocchi dice, which is a downside. However, thinking about the trade-off gave me an idea for another system based on a similar principle. The basic idea is to gamble on two independent dice both coming up high. So why not make stunts require success on two attack roles rather than one? This would still represent a single action, but would be similar to roll twice, take the lowest (since both need to hit). The essential dynamic of fighters being most able to benefit from stunts would be preserved, because (assuming the same level) fighters will have the best chance of hitting. This also seems like it would be easy to communicate to players: just make two attack rolls; no new mechanics would need to be introduced.