Is Impluse - Plusar effected by spell penetration?

Tasear · May 2017

Release a surge of elemental energy to deal [x] Magic Damage to nearby enemies and afflict them with Minor Mangle, which reduces their Max Health by 10% for 33 seconds.
Reduces enemy's Max Health.

I don't quite get how this works. I am starting to believe it might have something to do with spell penetration. As I seen even trial and dungeon bosses get this debuff, but mobs and dlc dugeons will hardly ever been effected when I am using plusar. So I ask how does it work? Is the plusar effected by spell penetration on mob or is simply chance?

Examples
vAA the ice giants can be debuffed
sometimes the garyloyes in vHRc are debuffed
wayrest 2nd boss can be debuffed
Worldbosses sometimes are debuffed.

BohnT · May 2017

There are some enemies which can be debuffed by this but others are immune. Spellpen only increases the damage of the aoe

Tasear · May 2017

BohnT wrote: »

There are some enemies which can be debuffed by this but others are immune. Spellpen only increases the damage of the aoe

That makes sense, I don't know what I was thinking. Thanks Still why does it sometimes work for some mobs and sometimes doesn't?

BohnT · May 2017

Tasear wrote: »

BohnT wrote: »

There are some enemies which can be debuffed by this but others are immune. Spellpen only increases the damage of the aoe

That makes sense, I don't know what I was thinking. Thanks Still why does it sometimes work for some mobs and sometimes doesn't?

Some Mobs are immune to certain effects. If you could debuff a boss by 10% of his max health it would be way too good so the implemented immunities resistances and weaknesses for the Mobs. Some take more poison damage like the 7th boss in VMsa others are immune to concussion like storm atronachs or the second boss in vAA or like the natural weakness of vampires for fire