Hi, I'm Treeston, and welcome to Combat PR Prep Refactors.

Today, we're moving UNIT_FLAG_IMMUNE_TO_PC and UNIT_FLAG_IMMUNE_TO_NPC to higher-level abstraction so combat manager can react to it.
New methods on Unit:
- void SetImmuneTo<All/PC/NPC>(apply, keepCombat = false);
- bool IsImmuneTo<All/PC/NPC>() const;

(cherry picked from commit 74af880217)

src/server/game/Entities/GameObject/GameObject.cpp

@@ -2101,7 +2101,7 @@ void GameObject::CastSpell(Unit* target, uint32 spellId, TriggerCastFlags trigge
         return;
 
     // remove immunity flags, to allow spell to target anything
-    trigger->RemoveUnitFlag(UnitFlags(UNIT_FLAG_IMMUNE_TO_NPC | UNIT_FLAG_IMMUNE_TO_PC));
+    trigger->SetImmuneToAll(false);
 
     if (Unit* owner = GetOwner())
     {