If you are doing good enough in a song, a rocket with a spiral tail will appear 
somewhere during the song. Successfully detonate that rocket, then successfully 
complete the song to unlock the new firework. Each song on each difficulty has 
its own unlockable firework, for a total of 30 unlockable firework types.

Code    - Effect
------------------------
8-ball - William Tell Overload, Easy Difficulty 
Apple with arrow through it - William Tell Overload, Hard Difficulty 
Bat - Valkyries Rising, Hard Difficulty 
Bizarre Creations logo (pumpkin) - Toccata and Funk, Medium Difficulty 
Butterfly - Rave New World, Medium Difficulty 
Cactus - William Tell Overload, Medium Difficulty 
Cherries - Game Over Beethoven, Medium Difficulty 
Cleff - Carmen Electric, Easy Difficulty 
Club Card - Rave New World, Easy Difficulty 
Crescent moon - Tail Light Sonata, Hard Difficulty 
Crown- Carmen Electric, Hard Difficulty 
Diamond card - Hall of the Mountain Dude, Easy Difficulty 
Dragon - Hall of the Mountain Dude, Medium Difficulty 
Dual musical note - Tail Light Sonata, Easy Difficulty 
Flower - Smooth Operetta, Hard Difficulty 
Guitar - 1812 Overdrive, Hard Difficulty 
Heart - Game Over Beethoven, Easy Difficulty 
Heart Card - Smooth Operetta, Easy Difficulty 
Jellyfish - Hall of the Mountain Dude, Hard Difficulty 
Llama - Valkyries Rising, Medium Difficulty 
Rocket ship - 1812 Overdrive, Medium Difficulty 
Saxophone - Rave New World, Hard Difficulty 
Seahorse - Game Over Beethoven, Hard Difficulty 
Single musical note - Toccata and Funk, Easy Difficulty 
Skull - Toccata and Funk, Hard Difficulty 
Smiley Face - Smooth Operetta, Medium Difficulty 
Snowflake - Tail Light Sonata, Medium Difficulty 
Spaceship - Carmen Electric, Medium Difficulty 
Spade card 1812 - Overdrive, Easy Difficulty 
Spider - Valkyries Rising, Easy Difficulty