Password screen 
Enter the options screen, select "Game Status", 
then press L1 + R1.

Special attacks
 
Interceptor Missiles 
Attack 1: Up, Up, Down, Machine Gun 
Attack 2: Up, Up, Up, Machine Gun 
Attack 3: Up, Up, Right, Machine Gun 

Bull's Eye Rockets 
Attack 1: Up, Down, Down, Machine Gun 
Attack 2: Up, Down, Up, Machine Gun 
Attack 3: Up, Down, Right, Machine Gun 

Sky Hammer Mortar 
Attack 1: Down, Down, Down, Machine Gun 
Attack 2: Down, Down, Up, Machine Gun 
Attack 3: Down, Down, Right, Machine Gun 

Brusier Cannon 
Attack 1: Down, Up, Down, Machine Gun 
Attack 2: Down, Up, Up, Machine Gun 
Attack 3: Down, Up, Right, Machine Gun 

Roadkill Mines 
Attack 1: Left, Right, Down, Machine Gun 
Attack 2: Left, Right, Up, Machine Gun 
Attack 3: Right, Left, Right, Machine Gun 

Brimstone Burner 
Attack 1: Right, Left, Up, Machine Gun 
Attack 2: Right, Left, Down, Machine Gun 
Attack 3: Right, Left, Right, Machine Gun