Misery

From WoW: IncGamers World of Warcraft Wiki

Talent: Misery
Effect: Your Shadow Word: Pain, Mind Flay and Vampiric Touch spells also cause the target to take an additional % spell damage.
Statistics: Rank 1 = +1%, Rank 2 = +2%, Rank 3 = +3%, Rank 4 = +4%, Rank 5 = +5%.