There was a typo in my formula, sorry I meant percent of damage, not chance.
It’s:
Actual Percent of Damage = Crushing Blow Percent ^ Rarity Level
Where Crushing Blow Percent = .25
In PvP, the Rarity Level of other players is 3
Yup, Crushing Blow is checked at the same time Crits are.
Each new target it hits will trigger onhit