Do arks you sacrifice to stun or heal power up this attack or just arks that are killed by an opponent?
They all count 
In pvp there’s a glitch where you don’t get the bonus.
You do get the bonus, it just doesn’t show in the moves description sometimes.
It’s only visual glitch, just like haste, timebomb at times etc.
But they all work…
Ok I was only wondering cuz sometime it only says it adds like 30%