How do you get all five sacred items on mythology island?

The five sacred items on Mythology Island are the flower, the ring, the pearl, the scale, and the whisker.

The Rare Flower (Rose - Garden of the Sphinx)

Climb up and open the aqueducts to flood the garden. Then you can get the rose.

The Minotaur Ring (Minotaur's Lair)

Use the reed pipe to enter the Labyrinth (the door opens with blue-blue-green-yellow-yellow-red-blue-green). Solve the bone riddle by spelling the Word TEN. Catch the red-eyed snake 3 times. The minotaur will give you his ring.

The Giant Pearl (Poseidon's Realm)

Enter the realm of Poseidon by offering the starfish from his statue in the Museum. Swim across the top, right side, and bottom of the maze to the Hydra cave. The giant clam is just above it.

The Hydra Scale (Hydra Cave)

When the Hydra attacks, jump up before he hits you. Land on each of the heads until all five are knocked out. Take the scale.

The Cerberus Whisker (Hades Realm)

Use the pomegranates from the Garden of the Sphinx as an offering to Hades. Cross the river Styx by avoiding the hazards. Use the reed pipe to lull Cerberus the watchdog to sleep (the song is blue-green-yellow-blue-red-green BUT you must get the song from the statue of Euterpe in the Temple of Muses). Take a whisker.

When you have all five items, see Athena at the Tree of Immortality.