Someone

L2CubicInstance

doAction()
....
case VIPER_CUBIC:
                _actionTask = ThreadPoolManager.getInstance().scheduleEffectAtFixedRate(new Action(30),
                                                                                        0, 20000)

.......

private class Action implements Runnable
    {
        private int _chance;

        Action(int chance)
        {
            _chance = chance;
            // run task
        }
         ......
        if( if (Rnd.get(1, 100) < _chance))
         .....
         useSkill(....);