Actually the damage reflect on all skills (HK's 'shield of revenge', GH's 'counterattack' and doombringer's 'eye for an eye') depends on (a) type of skill you are using, (b) your pdef and (c) enemy's p.atk.
If you attack salvatore (noob tank btw xD) with any skill like deadly blow that deals direct damage there is a chance to get a reflect (here it's VERY imbalanced I have never seen a server where reflect is 100% even in backstabs but w/e). In that moment you receive 2 or 3 instances of damage depending on your pdef and his p.atk as I mentioned earlier.
HK's skill last 5 mins and it has almost 100% chance to reflect here so when fighting a HK do not use skills that deal direct dmg. You can use bleed and bluff + all the debuffs. Still between the ToD and all the other skills it's almost impossible to kill a decent HK in oly, but hey welcome to toxic ;D.
GH's skill last 10 sec and works just like HK's skill.
And now the award for the most OP skill goes to:
Doombringer's skill return ANY instance of direct damage. Meaning that you can't even use normal attacks. Else you risk dealing 100 dmg and being reflected with 2k (you can literally lose a match in 2 second + sometimes the animation for casting 'eye for an eye' is cancelled so you don't see it and... well... gg xD).
Just as a side remark: even if I would like to have some things changed, I don't mind them the way they are. Who am I to speak anyway? A noob GH no? So don't take it personally when I say 2 out of the 3 mentioned skills are OP (leaving just my skill to be 'balanced' xD). I just want to explain to the poor soul how thing work here on l2toxic. Good luck Yosuf
