Accumulating Rupees:
Keep sailing around and defeat the jellyfish creatures. When they
split apart, destroy the remnants, collecting the multiple rupees.
Get Fire Sword: First acquire 10 Fairies; next, go to the Fairy Princess near the Sun Temple, where you will get the sword.
Mad Chickens: Start attacking the chickens in the towns, and you will see something interesting happen.
Locating Nintendo DS Island: Sail to the southwest part of the map, and you will find an island that resembles a Nintendo DS.
