What counts as low health for Killing Blow?

Question

Zero has a skill in the Bloodshed tree that

Massively increases Melee Damage against enemies with low health.

What exactly counts as low health in this case?

Answer 1

I initially guessed 50% health was considered "low health." If you were to melee attack light enemies (i.e., non-heavy enemies like most Bullymongs) at 50%, it would cause them to stagger. Though after experimenting, this doesn't seem to be the case.

Based on my observations, I'd say "low health" is ~33% health (or 1/3 health).

Fortunately, it is pretty clear when the ability was applied in a kill. Normally you deal a fixed amount of damage to everyone. When the ability is applied, you see a boost in the damage dealt and you get a nice "buzz" sound and a slashing animation for every hit.

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To test this, I respec'ed Zero and went off to fight making sure I didn't level up any more during the tests. As a baseline, I fought off enemies with only the Deception skill and no other skills. Every melee attack I dealt gave 55 damage.

I saved and restarted to go on another run. This time I added Killing Blow Level 1 to the mix. Again, most hits dealt 55 damage. Using a weak gun, I chipped enemies' health to around 50% (as close as I can get it) and hit them with a melee attacks. Still did 55 damage. I then tried for 25%. Again, as best as I can, I chipped them down to as close as I can to 25% then hit them with a melee attack. I got boosted damage and other indicators of a successful hit. So it's definitely applied at least at 25%.

However I noticed that at times when I wasn't quite at 25% but a little higher, I was still able to get the successful hit. So apparently it was higher. After a few more tests, I came to the conclusion that it is at 33% at max.

To see if the level of the skill affects this, I tried again with Killing Blow Level 2 and up. You get even more damage of course but it still seemed to apply at 33% and didn't change.