How to do that: a monster attack the monster on spawn

Java

just remove all barriers in monster's AI that doesnt allow it to hit other monster.

well here is, im using it on my serv and works perfectlly, try to rework for your core,

 

add this onSPawn
npc.broadcastPacket(new AutoAttackStart(npc.getObjectId()));
ThreadPoolManager.getInstance().scheduleAi(new AttackTask(npc, TARGET_ON_WHICH_YOUR_NPC ATTACKS), Rnd.get(10, 1000));



private static final class AttackTask implements Runnable
{
	private final L2Npc _attacker;
	private final L2Npc _target;
	public AttackTask(L2Npc attacker, L2Npc target)
	{
		_attacker = attacker;
		_target = target;
	}
	@Override
	public void run()
	{
		Broadcast.toPlayer(new Attack(_attacker, _target, false, 0, true), _attacker.getInstanceId());
		ThreadPoolManager.getInstance().scheduleAi(new AttackTask(_attacker, _target), 1500);
	}
}