This is my first attempt at writing a walkthrough, so here it goes!
1) Go to Shark Tooth Island and obtain carbonated coconut milk from the man outside the cafe.
2) Go right to the temple ruins. Push the square block under the vines at the far right and climb them, avoiding the coconuts. Jump onto the temple roof to get the translation key.
3) Enter the temple and make your way to the top left corner by jumping onto platforms and avoiding the bats. Use the translation key to spell the word “OPEN” on the keypad and then press the nose. A secret passageway should open up.
4) Jump left onto the platform with ‘Batman’ on it. Jump left again onto the golden shark statue and up to the top. Be wary of the giant caterpillars; they might knock you down. Once you are at the top of the statue, jump onto the swinging platform and over to the left where you will see a sliding platform.
5) Don’t walk onto the sliding platform just yet. First you will need to fall down into the spiked chasm, where you will find an old bone. Go to the right and jump onto the statue again, repeating what you did in step #4. This time,use the sliding platform to go left to the temple treasure room. When you are there, take the secret ingredient and climb up the vine to Main Street.
6) Go past the temple ruins and to Booga Bay, where you will obtain a grass skirt from a salesman. A crying woman will tell you that she has lost her son. Put on the grass skirt and go back to the Temple Ruins. Climb up the vines and meet the Medicine Man, who will give you a special mixture inside a coconut that will put the Booga (a giant shark terrorizing the island) to sleep.
7) At Booga Bay, use the cannon to feed the coconut to Booga.
Swim across the bay to an island at the right, where you will find Professor Hammerhead and the boy. Lead them back to shore, and you will get the island medallion. Congratulations! You’ve completed the island.