Unlocking Sky Roost (World 8)
To Unlock Sky Roost You must collect all five Tori birds hidden in the game. These birds are hidden in each of the Worlds (besides World 4 and 6) in one level. You will always come across these birds by finding a "cloud ground" portion part in a level. At the end of this "cloud portion" you will come across an egg which you must hit to obtain the bird. Each Tori is located in the following songs if you press the Y Button: The 4th level of World 1, the 6th level of World 2, the 7th level of World 3, the 8th level of World 5 (unlocked after beating the game), and the 3rd level of world 7. Once you obtain all the Tori, go back to Symphony City and head for the locked door near the city and you will be able to unlock the door and head into the hidden final world.
To unlock the following songs, you must complete certain worlds then select the song from the song selection list by pressing Y and shifting the song lists all the way to the left.
Bicycle Theme (Gold/Silver) - Complete Calypso Beach (World 3)
Champion Theme (Red/Blue) - Complete Sleighbell Mountains (World 5)
Pokemon Gym Theme - Complete Marching Hills (World 1)
Route 26 Theme (Gold/Silver) - Complete Rock Range (World 2)
Trainer Battle Theme (Black/White) - Complete Baroque Valley (World 7)