I suggest checking in "/stagehands/mission/apexmissionbattleeffect.stagehand". This looks like a stagehand which makes the above-ground NPCs invulnerable so that the "battle" doesn't end prematurely. Probably just making a copy of the stagehand and it's script, then repurposing it for yourself, should work. The .stagehand file allows you to change the broadcastArea, affected entityTypes, and the effect. (Not too sure what the eftectCategory is for...)