Once Athena has talked to you about Zeus, you just visit Hercules and select the 2nd and 3rd options, and select all the ones you have unlocked.
Hercules will help you reach the throne rooms of Poseidon and Hades. But you need the Touchscreen Mirror from Aphrodite's test in Poseidon's realm.
you need to talk to athena, and she says ask hercules again, and then he will come with you if you have the touchscreen mirror, and he will open the border for you.
You don't need an autograph. After you get the five items, go to the Tree of Immortality, where Zeus will steal the items from you. Then Hercules will agree to help you. You will need the Touchscreen mirror from Aphrodite (on the beach in Poseidon's realm).
Hercules is signing autographs at Herc's Hero Hut on Main Street. Nothing in the place has any function whatsoever in the island quest. Hercules will only help you after Zeus has obtained the five sacred items and threatens to control Poptropica. You will need the Touchscreen Mirror from Aphrodite's test (on the beach in the realm of Poseidon).
To play the game faster (and to satisfy lazy Hercules) , you will need the Touchscreen Mirror from Aphrodite. You will find her in Poseidon's realm, on the beach. If you pass her test, you will get a transporter mirror. Answers for the test : Ares, Hermes, Aphrodite, Artemis, and Hestia.
After you collect all five sacred items, return to the Tree of Immortality. Zeus will take them. Then you can go to Hercules and talk to him. Use the Touchscreen Mirror to teleport to Hades throne room and Hercules will move the boulder.
You don't need to defeat him. Athena said he would help, but only for the final stages. Find the 5 sacred items and return them to the Tree of Immortality. Get the Touchscreen Mirror from Aphrodite's test, as Hercules does not like to walk very far.
No just mythology island
You have to get Hercules to help you. But he won't until you have returned the 5 sacred items to the Tree of Immortality. After Zeus steals them, Hercules will help you reach Hades and Poseidon to get their help. You will need the Touchscreen Mirror from Aphrodite's test. (see related question)
The third choice after you get all of the sacred items.
Hercules will not help you until you have collected the 5 sacred items and had them stolen by Zeus. You will need the Touchscreen Mirror from Aphrodite's test on the beach. Transport yourself with Hercules to the Hades door and he will roll back the big rock. He will do the same for the rock blocking Poseidon's throne room.
Hercules will not help you get the 5 sacred items. You have to get all 5 items and return to the Tree of Immortality to see Athena. When you have deciphered the hidden message, Zeus seizes the items from you. Now Hercules will help you reach the thrones of Poseidon and Hades. But you need the Touchscreen Mirror from Aphrodite's test in Poseidon's realm.