How do you defeat Cerberus on mythology island?

You will need a reed pipe (Flute) and a song from the Temple of the Muses. Playing the short song will lull the monster dog to sleep. (the song is blue-green-yellow-blue-red-green)

1. Go right to the Temple Grove and enter the temple of the Muses.
2. At far right are the "free reeds".
3. Go to the statue of Euterpe (muse of music)
4. Pass the test by matching the 8-note melodies on the reed pipe.
5. You receive the card with the 6-note song to lull Cerberus.

When you enter the realm of Hades from his temple, you will ride the River Styx to Hades domain. When you meet Cerberus, play the song (blue-green-yellow-blue-red-green) and you can take a whisker when he falls asleep.