What are the notes to make the Hydra fall asleep on Mythology Island?

The reed pipe is to make Cerberus fall asleep. You are a lot less gentle with the Hydra. Get close enough and it will try to hit you with one of its five heads. Before it can hit you, jump up, and land on the head when you come down. Repeat this for the remaining heads before any can revive. Swim under the Hydra to get a scale.