make a blueprint interface, call it iMortal, and define some functions for it, like TakeDamage, InstaKill, Heal, Burn, CauseStatusEffect, etc… then make a character or actor that implements that interface, in its class settings. then you can define those interface functions for that actor, allowing them to change their own health or set other variables.
then you can make an actor that causes damage on overlap, getting the OtherActor, and calling one of the iMortal damage functions on it.