I know Draught of Souls has a factor for mastery scaling for UH, eventually given a 30% damage reduction by Blizzard, so I was curious about the mastery scaling for UH with Specter of Betrayal. At 77% mastery, my plain 910 Specter of Betrayal tooltip says it should do 740,806 shadow damage over 3 seconds. This number will change as my mastery goes up or down (with 375 mastery food and 79% mastery, it increases to 749,632). However, I am seeing overall damage fluctuations between ~560k and about ~760k. Without changing any stats or getting any active buffs, I've been testing it 1 minute apart just to check the overall damage it says it's supposed to do, I've tried to make sure it's against a single target, moved in and out to various melee ranges, and I'm continuing to see these damage fluctuations. For more details : teaser trailer