You have to cross the River of Styx, play the tune the goddess gave you to play on your reed pipe, then click on the Cerberus to get the whisker. Hope that helps!! =)

That island is so hard!! If you look on youtube there are a couple of videos there. Try typing in mythology island on poptropica and the person who made it name is secretscp. Hope HE helps you!! I don't know jack squat about beating this game!!