The Legend of Zelda: Four Swords/Unlockables

Unlock Sword Beams
Simply retrieve the Master Sword in A Link to the Past.

Unlock the Riddle Quest
To unlock the Riddle Quest succesfully you must obtain 10 Triforce Medalions.

Unlock the Hurricane Blade
Complete the Riddle Quest in A Link to the Past. It will then be available in both games.

Unlock the Palace of the Four Sword
You must beat Vaati at least once in order to be "a true hero".