Core/Scripts: fix Nightfall proc chance and reduce it for victims with level above 60

Closes #15734

(cherrypicked from eac9c1f0b9)

src/server/scripts/World/item_scripts.cpp

@@ -414,6 +414,30 @@ public:
     }
 };
 
+// Only used currently for
+// 19169: Nightfall
+class item_generic_limit_chance_above_60 : public ItemScript
+{
+    public:
+        item_generic_limit_chance_above_60() : ItemScript("item_generic_limit_chance_above_60") { }
+
+        bool OnCastItemCombatSpell(Player* player, Unit* victim, SpellInfo const* /*spellInfo*/, Item* /*item*/) override
+        {
+            // spell proc chance gets severely reduced on victims > 60 (formula unknown)
+            if (victim->getLevel() > 60)
+            {
+                // gives ~0.1% proc chance at lvl 70
+                float const lvlPenaltyFactor = 9.93f;
+                float const failureChance = (victim->GetLevelForTarget(player) - 60) * lvlPenaltyFactor;
+
+                // base ppm chance was already rolled, only roll success chance
+                return !roll_chance_f(failureChance);
+            }
+
+            return true;
+        }
+};
+
 void AddSC_item_scripts()
 {
     new item_only_for_flight();
@@ -427,4 +451,5 @@ void AddSC_item_scripts()
     new item_dehta_trap_smasher();
     new item_trident_of_nazjan();
     new item_captured_frog();
+    new item_generic_limit_chance_above_60();
 }