Begin a new game with the name B4K42. Hit pause during the game to find the selection for God Mode. Here, you can turn it on and off.
Large Ship Kills
To take down larger ships, land on them and use grenades or pulsars. Drop ships can't reach you while you are positioned on top, standing between the automatic turrets. This strategy doesn't work against Fenrir, which has turrets that can fire on all sides, but otherwise it's a great technique that has the added benefit of allowing you to replenish your energy while you inflict damage. Just make sure that you fly away the second the ship is finally destroyed.
Unlock Every Stage
To unlock all of the stages in Campaign Mode, begin a new game with the name !EVAH! (including the exlamation points and capital letters).
Unlock Everything In Gallery
Start a new game with the name 105770Y2. This should unlock everything in the gallery.