Watersweep and Windsweep?

I'm curious too. I tried a lot of theory craft and didn't find any hero who would benefit more from this skill than others B skills.

It's also a big question mark for me, but that's mostly because I never really tried to think about it. I guess that a hero with speed around 30 would be the best fit, because you don't want to put it on a speedy unit, because it disables follow-ups. So a unit that almost never doubles would be pretty ok and that 30 speed probably the optimal value that I would recommend, because many other heroes have 34 speed, which would be the sweet spot with phantom speed.

Imo it could be used with high speed Blade tome users but they lose out on a double which is kinda bad in that way, or it Brave bow archers since the brave bow will automatically double but u might lose the chance to quad. If u have a 27-30ish unit with more than 35 attack he/she could utilize the skill to its fullest in good conditions. I would prefer Wind sweep on mages to counter distant counter(minus bow and dagger)and vantage though not watersweep.

One of the best users is F Corrin with dark breath. Attack with dark breath, debuff everyone without retaliation, use a skill like Drag Back to isolate the unit to target, and finish it off.