Priest · Shadow Magic · tier 6 · from level 35

Darkness

+82.7 Devouring Plague

5/5 · level 60 · per cast · and 4 more

Darkness 12345

Rank 5/5

Increases your Shadow damage done by 10%.

Devouring Plague +10.0% +82.7 Shadow Word: Pain +10.0% +74.3 Mind Blast +10.0% +47.8 Shadow Word: Death +10.0% +44.7 Mind Flay +10.0% +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.