I dont understand the point of useing Blood Presence over Unholy Presence.
It increases damage by 15% and heals you for 2% of the damage, but the problem is that fact that the attacks do too little damage to justify that added damage over the faster attacks and shorter GCD of Unholy Presence.
The healing from this effect is also very weak. At low lvls like 55 it could be a bit useful, but once the HP to Damage ratio starts to shift more towards HP, then the healing becomes very lame. :-X :-\
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I could understand something like this on a more bursty type melee class like Paladins and Warriors, but I cant see this more useful or a attack spammer like Death Knights and rogues.
Unholy Presence is just plain old better in every way.
And yes I am Blood Spec, but I find that I dish out better damage from Unholy Presence because I can get off Diseases faster, and begin spamming my more Damage oriented attacks.