Wynn Spectral Master skill Curse Exposure

Hi,
I have a question regarding Wynn lvl 99 skill Curse Exposure: Attacks the target with M. Atk. +249. For 30 seconds, Deadly Attack Def. -30%. Consumes 1 Spirit Ore.
What is deadly attack def?
Also Wynn EM has the skill for -pdef/mdef. Usualy i play with an iss boxed for debufs and marks on. Should i change to EM, or the mark+iss debufs is enough in pve?
Ty

 

mark + iss debuff is already more then cap of p/m def of mob you can remove.
At lest as far as I remember from tests in forum (-50% is max).

 

lvl 100 pet (dark crusader) have one skill name Phantom blow (this skill give same lethal as dagger) this deadly attack is for increase chance of this lethal enter !
Skill of elmental master is good because remove elemental resistance... (pdef and mdef have cap on mob for remove, but elemental not..) (so u will do more damage on pve)

 

And IMO +20% critical damage > 20% p attack.