Shadow Weaving

From wow.incgamers.com

Talent: Shadow Weaving
Effect: Your Shadow damage spells have a % chance to cause your target to be vulnerable to Shadow damage. This vulnerability increases the Shadow damage dealt to your target by 2% and lasts 15 sec. Stacks up to 5 times.
Statistics: Rank 1 = 20%, Rank 2 = 40%, Rank 3 = 60%, Rank 4 = 80%, Rank 5 = 100%.