Feeding on a major spirit,ever tried?

i have before used a “god of hunger” sort of egregore with vampirism in a sort of attack ritual. you would be surprised depending on the person how quickly this can give them bad health. but I wonder,if this egregore fueled vampirism can damage a person,what would a coordinated effort shared between more than one person do to a major spirit like an arch angel or a greater daemon?