How do you get the flute on Cryptids Island?

The reed pipe comes from inside the Temple of Muses in the Grove of Temples. Play it by pressing any of the four colored holes (notes). The statue of Euterpe inside the temple will give you a song to use if you pass her musical memory test.

There are only two times you use the reed pipe (Flute). One is to open the door to the Minotaur's lair in the Garden of the Sphinx. The order (blue-blue-green-yellow-yellow-red-blue-green) is shown on the circular pattern on the door. The second use is to lull the dog-beast Cerberus in the realm of Hades. Playing the tune ( blue-green-yellow-blue-red-green) will make him snooze and you can grab a whisker from him (one of the 5 sacred items).