How to play the black holy water in the mushroom temple of Adventure Island?

NPC dark undead place receives the task of black holy water. Hit 20 black snake venom on the map on the right and hand in the task to get black holy water. NPC dark undead place receives the task of black holy water. Hit 20 black snake venom on the map on the right and hand in the task to get black holy water. NPC dark undead place receives the task of black holy water. Hit 20 black snake venom on the map on the right and hand in the task to get black holy water. NPC dark undead place receives the task of black holy water. Hit 20 black snake venom on the map on the right and hand in the task to get black holy water. NPC dark undead place receives the task of black holy water. Hit 20 black snake venom on the map on the right and hand in the task to get black holy water. NPC dark undead place receives the task of black holy water. Hit 20 black snake venom on the map on the right and hand in the task to get black holy water.