Priest · Shadow Magic · tier 4 · from level 25

Shadow Weaving

+82.7 Devouring Plague

3/3 · level 60 · per cast · estimate: 5 Shadow Weaving stacks · and 4 more

Shadow Weaving 123

Rank 3/3

Your Shadow damage spells have a 100% chance to increase the Shadow damage you deal by 2% for 15 sec, stacking up to 5 times.

Devouring Plague +82.7 Shadow Word: Pain +74.3 Mind Blast +47.8 Shadow Word: Death +44.7 Mind Flay +38.0

Averages, counting crits and misses, for a level 60 Priest with a typical weapon and no other gear or buffs, against a target your level. Worked out from the game's own data, the same way as the Foresight addon.