If you have a joystick with auto-fire, set C to rapid auto-fire while shooting with B. Your ship will fire all available weapons at once!
Full Weapons
To recharge your weapons while playing, pause the game and press Up 10 times, B, Down, Down, B until the weapon meter is full. To add "The Claw" to your arsenal, press A. Unpause the game and fire at will.
Options
At the title screen, hold A + B + C, then press Start. This brings up a screen allowing the selection of ship speed, difficulty, more.
Two-Player Mode
If you have two controllers, two players can control the same ship. This is convenient if you want to take turns flying and allows one player to man the guns while the other navigates.
Waving Credits
At the credits screen hold C. One of the kids will wave and wink at you.