As far as I've noticed, auras/zones deal 2% of total stun (Death's black zone) or 1% of total health (Servant's red zone). It's the reflect that does massive damage from either.
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That's one of the things I tried initially before beating the death raid, it didn't work. I tried a bunch of things, but Evangelion-01's suggestion saying to use stake sets is what made the objective difference in actually completing the raid.
Would be cool if that new golden cross (furniture), allows for either stunning them or if placed near cages to tame them or something... but its probably just a placeholder for something else for now though.