Double post due to forum glitch. But let's recap.
For duel to work you need to use a single, one-handed melee weapon. Four things are off the table: ranged weapons, two-handed weapons, dual wielding weapons, versatile weapons with an empty off-hand. I'm still saying that a few words to explain the weirdness around versatile weapons and the empty off-hand will make things clearer than the convoluted, if technically correct, sentence.
edit : Crud, I've got so much work to do but I can't not think about this. Final answer:
"+2 damage when using a single one-handed melee weapon (versatile weapons are held with both hands if the off hand is empty)"
Last edited by Flooter; 05/09/23 04:28 PM. Reason: still thinking about this...