fix(Core/Unit): Reduce mobs speed when low on health (#7932)

src/server/game/Entities/Creature/Creature.cpp

@@ -1805,7 +1805,6 @@ void Creature::setDeathState(DeathState s, bool despawn)
         if (HasSearchedAssistance())
         {
             SetNoSearchAssistance(false);
-            UpdateSpeed(MOVE_RUN, false);
         }
 
         //Dismiss group if is leader

src/server/game/Entities/Unit/Unit.cpp

@@ -9773,7 +9773,6 @@ bool Unit::AttackStop()
         if (creature->HasSearchedAssistance())
         {
             creature->SetNoSearchAssistance(false);
-            UpdateSpeed(MOVE_RUN, false);
         }
     }
 
@@ -13496,11 +13495,23 @@ void Unit::UpdateSpeed(UnitMoveType mtype, bool forced)
             break;
     }
 
-    // for creature case, we check explicit if mob searched for assistance
-    if (GetTypeId() == TYPEID_UNIT)
+    int32 slowFromHealth = 0;
+    Creature* creature = ToCreature();
+    // ignore pets, player owned vehicles, and mobs immune to snare
+    if (creature
+        && !IsPet()
+        && !(IsControlledByPlayer() && IsVehicle())
+        && !(creature->HasMechanicTemplateImmunity(MECHANIC_SNARE))
+        && !(creature->IsDungeonBoss()))
     {
-        if (ToCreature()->HasSearchedAssistance())
-            speed *= 0.66f;                                 // best guessed value, so this will be 33% reduction. Based off initial speed, mob can then "run", "walk fast" or "walk".
+        // 1.6% for each % under 30.
+        // use min(0, health-30) so that we don't boost mobs above 30.
+        slowFromHealth = (int32) std::min(0.0f, (1.66f * (GetHealthPct() - 30.0f)));
+    }
+
+    if (slowFromHealth)
+    {
+        AddPct(speed, slowFromHealth);
     }
 
     // Apply strongest slow aura mod to speed
@@ -14566,8 +14577,16 @@ void Unit::SetHealth(uint32 val)
             val = maxHealth;
     }
 
+    float prevHealthPct = GetHealthPct();
+
     SetUInt32Value(UNIT_FIELD_HEALTH, val);
 
+    // mobs that are now or were below 30% need to update their speed
+    if (GetTypeId() == TYPEID_UNIT && (prevHealthPct < 30.0 || HealthBelowPct(30)))
+    {
+        UpdateSpeed(MOVE_RUN, false);
+    }
+
     // group update
     if (GetTypeId() == TYPEID_PLAYER)
     {

src/server/game/Movement/Spline/MoveSplineInit.cpp

@@ -115,9 +115,6 @@ namespace Movement
                 moveFlagsForSpeed &= ~MOVEMENTFLAG_WALKING;
 
             args.velocity = unit->GetSpeed(SelectSpeedType(moveFlagsForSpeed));
-            if (Creature* creature = unit->ToCreature())
-                if (creature->HasSearchedAssistance())
-                    args.velocity *= 0.66f;
         }
 
         // limit the speed in the same way the client does