Answered
I've played Pantheon a lot recently, so I know that his Q deals more damage to targets below 20% health, and the lolwiki page does confirm this.
The problem is, it doesn't say how much the damage is increased.
Is it just an execute at this point? It seems like it, but it's very unclear.
Ehhhh2 votesINCREASED DAMAGE:» 155 / 240 / 325 / 410 / 495 (+ 200% bonus AD)
Click on the 'physical damage' button and it will show you increased damage
Elite4Runner1 votesAh, I see. I forget that they have that toggle-able sometimes. [zombie-brand-facepalm]
Thanks!
xDogMeatx1 votesits a crit strike on Q.
Elite4Runner1 votesClose, but not exactly.
It is 206.7% / 218.2% / 224.1% / 227.8% / 230.2% base + 200% BONUS AD
So more than double on the base damage, but only double BONUS AD.
A champion with less than 2475 maximum health that is below 20% HP will be on less than 495 health, which is the base damage at rank 5.
So as long as the bonus damage covers their resistances, they're dead.