Core/Threat: Assistance threat (healing, buffs, etc.) is now properly split (instead of copied) between all creatures threatened by the action. Thanks to Foereaper for help with testing, and my apologies to healers everywhere.

(No apologies for charm AI though. You deserve that one.)

src/server/game/Combat/ThreatManager.cpp

@@ -608,8 +608,11 @@ void ThreatManager::ForwardThreatForAssistingMe(Unit* assistant, float baseAmoun
 {
     if (spell && spell->HasAttribute(SPELL_ATTR1_NO_THREAT)) // shortcut, none of the calls would do anything
         return;
+    if (_threatenedByMe.empty())
+        return;
+    float const perTarget = baseAmount / _threatenedByMe.size(); // Threat is divided evenly among all targets (LibThreat sourced)
     for (auto const& pair : _threatenedByMe)
-        pair.second->GetOwner()->GetThreatManager().AddThreat(assistant, baseAmount, spell, ignoreModifiers);
+        pair.second->GetOwner()->GetThreatManager().AddThreat(assistant, perTarget, spell, ignoreModifiers);
 }
 
 void ThreatManager::RemoveMeFromThreatLists()