
Mangle is working, it's just applying after the damage of incap strike, rendering it useless.
Let's say an enemy has 50k health. Your incap does 10k dmg.
Hitting an enemy without the mangle reduces his hp to 40k.
Hitting an enemy with minor mangle reduces his hp to 40k hp on account of the damage from incap, but also reduces his max hp to 45k hp. This goes entirely unused, however, because incap itself is doing more than 10% of the targets health, leaving only empty health bar for the mangle to reduce.
It is indeed working, its just completely useless in its current form. Even if they change it so that the mangle applies before the damage of incap, its usefulness is still extremely limited.
Let's take the same example, but pretend that minor mangle applies before the incap damage. The 50k hp would be reduced to 45k from the mangle, then the 10k incap damage would further reduce his health to 35k.
This would result in a net gain 5k dmg (10% of the targets health).
This of course assumes that an nb uses incap on a full health target. If the nb uses incap on a target with less than 90% health remaining, mangle will be wasted on empty health bar, similar to what is currently happening on PTS with the mangle applying after the damage.
That means that in order for minor mangle to be of any use to an nb, they must use incap strike as their opening move, which hardly ever happens. Especially because the 8% dmg bonus in an nbs toolkit is now tied to ambush in the form of minor vulnerability.
This encourages nbs to use ambush before incap, but at the same time renders the minor mangle on incap useless because in almost all scenarios ambush would deal at least 10% of the enemies health bar, leaving mangle to be wasted on only empty health bar.
Additionally, mangle reducing an enemies max hp also inherently reduces the execute range on abilities. This is evidenced by 50% (the execute range of poison injection) of 50k hp being 25k hp, and 50% of 45k hp being 22.5k hp.
So mangle is not only being completely wasted, but it is also decreasing the damage of executes against a mangled target. This supposed "debuff" is actually helping the enemy.
Mangle is a very very poorly thought out addition to this skill.