I would probably cry if someone did this to me, I think the Necron player in this video held himself together quite well but you could tell he was miffed.
https://www.youtube.com/watch?v=EwnYrSEMLeY
Basically, at the beginning of the 2nd turn, the Necron player spent the
CP on extermination protocols, but the Custodes player totally nullified it with Emperors Auspice.
Extermination Protocols (1CP): Use this Stratagem in your Shooting phase before shooting with a Destroyer Lord, a unit of Destroyers or a unit of Heavy Destroyers from your army. Re-roll failed hit and wound rolls for that unit until the end of the phase.
The Emperor’s Auspice (2CP): Use this Stratagem in any phase, when an Adeptus Custodes unit from your army is chosen as the target of an attack. Until the end of that phase, when resolving an attack against that unit your opponent cannot reroll any dice for that attack.
Is there any get out for the Necron player to be able to play this card, which is one of their more powerful cards or is it basically useless when going against Custodes?
Having thought about it, I guess he needs to split fire and have the Custodes player decide who they want to protect.