Index: dist/game/config/Custom/MonsterSpawnMultiplier.ini
===================================================================
--- dist/game/config/Custom/MonsterSpawnMultiplier.ini  (nonexistent)
+++ dist/game/config/Custom/MonsterSpawnMultiplier.ini  (working copy)
@@ -0,0 +1,16 @@
+# ---------------------------------------------------------------------------
+# Monster Spawn Multiplier
+# ---------------------------------------------------------------------------
+
+# Enable/Disable monster spawn multiplier.
+# Default: False
+MonsterSpawnMultiplierEnable = False
+
+# Monster spawn count will be multiplied with this number.
+# Default: 1
+MonsterSpawnMultiplierRate = 1

+# Monster spawn mode
+# 0 : static (fixed rate MonsterSpawnMultiplierRate)
+# 1 : dynamic (random from 1..MonsterSpawnMultiplierRate)
+# Default: 0
+MonsterSpawnMultiplierMode = 0

+# Specify ids of monsters to be affected, or leave empty to affect all monsters.
+# Example:
+# MonsterMultiplierList = 1045, 2019
+MonsterSpawnMultiplierList =

Index: java/com/l2jmobius/Config.java
===================================================================
--- java/com/l2jmobius/Config.java  (revision 5007)
+++ java/com/l2jmobius/Config.java  (working copy)
@@ -118,6 +118,7 @@
    private static final String CUSTOM_FACTION_SYSTEM_CONFIG_FILE = "./config/Custom/FactionSystem.ini";
    private static final String CUSTOM_FAKE_PLAYERS_CONFIG_FILE = "./config/Custom/FakePlayers.ini";
    private static final String CUSTOM_FIND_PVP_CONFIG_FILE = "./config/Custom/FindPvP.ini";
+   private static final String CUSTOM_MONSTER_MULTIPLIER_CONFIG_FILE = "./config/Custom/MonsterSpawnMultiplier.ini";
    private static final String CUSTOM_MULTILANGUAL_SUPPORT_CONFIG_FILE = "./config/Custom/MultilingualSupport.ini";
    private static final String CUSTOM_NPC_STAT_MULTIPIERS_CONFIG_FILE = "./config/Custom/NpcStatMultipliers.ini";
    private static final String CUSTOM_OFFLINE_TRADE_CONFIG_FILE = "./config/Custom/OfflineTrade.ini";
@@ -1076,6 +1077,9 @@
    public static boolean FAKE_PLAYER_CAN_DROP_ITEMS;
    public static boolean FAKE_PLAYER_CAN_PICKUP;
    public static boolean ENABLE_FIND_PVP;
+   public static boolean MONSTER_SPAWN_MULTIPLIER_ENABLED;
+   public static float MONSTER_SPAWN_MULTIPLIER_RATE;
+   public static float MONSTER_SPAWN_MULTIPLIER_MODE;
+   public static List<Integer> MONSTER_SPAWN_MULTIPLIER_LIST;
    public static boolean PREMIUM_SYSTEM_ENABLED;
    public static float PREMIUM_RATE_XP;
    public static float PREMIUM_RATE_SP;
@@ -2430,6 +2434,22 @@
            final PropertiesParser FindPvP = new PropertiesParser(CUSTOM_FIND_PVP_CONFIG_FILE);
            ENABLE_FIND_PVP = FindPvP.getBoolean("EnableFindPvP", false);

+           // Load MonsterSpawnMultiplier config file (if exists)
+           final PropertiesParser MonsterSpawnMultiplier = new PropertiesParser(CUSTOM_MONSTER_MULTIPLIER_CONFIG_FILE);
+
+           MONSTER_SPAWN_MULTIPLIER_ENABLED = MonsterSpawnMultiplier.getBoolean("MonsterSpawnMultiplierEnable", false);
+           MONSTER_SPAWN_MULTIPLIER_RATE = MonsterSpawnMultiplier.getFloat("MonsterSpawnMultiplierRate", 1);
+           MONSTER_SPAWN_MULTIPLIER_MODE = MonsterSpawnMultiplier.getInt("MonsterSpawnMultiplierMode", 0);
+           final String[] monsterSpawnMultiplierList = MonsterSpawnMultiplier.getString("MonsterSpawnMultiplierList", "").split(",");
+           MONSTER_SPAWN_MULTIPLIER_LIST = new ArrayList<>(monsterSpawnMultiplierList.length);
+           for (String monsterId : monsterSpawnMultiplierList)
+           {
+               monsterId = monsterId.trim();
+               if (!monsterId.equals("0") && Util.isDigit(monsterId))
+               {
+                   MONSTER_SPAWN_MULTIPLIER_LIST.add(Integer.parseInt(monsterId));
+               }
+           }
+
            // Load MultilingualSupport config file (if exists)
            final PropertiesParser MultilingualSupport = new PropertiesParser(CUSTOM_MULTILANGUAL_SUPPORT_CONFIG_FILE);

Index: java/com/l2jmobius/gameserver/model/spawns/NpcSpawnTemplate.java
===================================================================
--- java/com/l2jmobius/gameserver/model/spawns/NpcSpawnTemplate.java    (revision 5007)
+++ java/com/l2jmobius/gameserver/model/spawns/NpcSpawnTemplate.java    (working copy)
@@ -25,6 +25,7 @@
 import java.util.logging.Level;
 import java.util.logging.Logger;
+import java.util.Random;

+import com.l2jmobius.Config;
 import com.l2jmobius.commons.util.Rnd;
 import com.l2jmobius.gameserver.data.xml.impl.NpcData;
 import com.l2jmobius.gameserver.datatables.SpawnTable;
@@ -87,7 +88,7 @@
        _spawnTemplate = spawnTemplate;
        _group = group;
        _id = set.getInt("id");
-       _count = set.getInt("count", 1);
+       _count = getSpawnMultiplier(_id, set);
        _respawnTime = set.getDuration("respawnTime", null);
        _respawnTimeRandom = set.getDuration("respawnRandom", null);
        _spawnAnimation = set.getBoolean("spawnAnimation", false);
@@ -128,6 +129,21 @@
        mergeParameters(spawnTemplate, group);
    }

+       private int getSpawnMultiplier(int id, StatsSet set)
+       {
+               final int originalCount = set.getInt("count", 1);
+               if (Config.MONSTER_SPAWN_MULTIPLIER_ENABLED && NpcData.getInstance().getTemplate(id).isType("L2Monster"))
+               {
+                       int newSpawnCount = originalCount;
+                       if (Config.MONSTER_SPAWN_MULTIPLIER_MODE == 1)
+                       {
+                               newSpawnCount = newSpawnCount * (new Random().nextInt((int) ((Config.MONSTER_SPAWN_MULTIPLIER_RATE - 1) + 1)) + 1);
+                       }
+                       else
+                       {
+                               newSpawnCount = (int) (newSpawnCount * Config.MONSTER_SPAWN_MULTIPLIER_RATE);
+                       }
+
+                       if (!Config.MONSTER_SPAWN_MULTIPLIER_LIST.isEmpty())
+                       {
+                               return Config.MONSTER_SPAWN_MULTIPLIER_LIST.contains(id) ? newSpawnCount : originalCount;
+                       }
+                       return newSpawnCount;
+               }
+               return originalCount;
+       }