I agree with @TakeWalker and @Rabit’s readings of the Ability. I, too, thought it read “once per round,” for the longest time. Perhaps it is a typo (and someone should bring that to the attention of the appropriate persons), but until proven wrong, I think we should interpret its wording exactly.
As for @catDreaming’s interpretations of the Ability’s benefits:
- I agree with this first point’s effect, although I think I would rephrase it is, “You may use 1 Reaction per turn, instead of per round, for free.”
- I would argue that the damage-or-twist happens after the extra Reaction, because the Ability reads, “Each time,” which to me implies a triggered action, and an action cannot happen before its trigger. Plus, it lets a Hero make a Noble Heroic Sacrifice.