public void Remove(ISpawnable spawn)
        {
            if (Spawn != null && Spawn.Contains(spawn))
            {
                Kills++;
                Spawn.Remove(spawn);

                if (Kills >= KillsPerWave)
                {
                    if (Level >= Levels)
                    {
                        EndSimulation();
                        return;
                    }
                    else
                    {
                        IncreaseLevel();
                    }
                }

                Timer.DelayCall(NextSpawnDuration, DoSpawn);
            }
        }