burzolog asked: Did Mercer tell Laura that the spell Delilah cast on Vex could have killed her instantly? The spell was almost certainly Finger of Death, and it could have taken her straight to 0 hp, but it couldn't have overkilled her by her max hp. Does the zombie animation effect override the normal process of going unconscious and rolling death saves? I don't see why it would work that way.
Matt explained that the spell was Finger of Death after Delilah cast it (ep25, 1:04:33). He also clarified in the latest episode (29) during the NYCC panel (11:36) that the spell would have killed her outright, had it brought her to 0 hp. The spell’s description does explain that it overrides the death-saving process, and the victim is immediately turned into a zombie in the next round under the caster’s control. No saves, automatic game over; specific rules override general rules. Vex was lucky Lady Briarwood cast it when she was at full health!
The good news is that it is unlikely Delilah can cast it more than once per day. The other good news is that no other necromancy spell has this property of bypassing the unconsciousness state. The bad news is that the bite of vampire can also bypass this state, provided it is the bite that takes the victim to 0 hp.