From StrategyWiki, the free strategy guide and walkthrough wiki

• When Takky gets hit with the Machine Gun Vessel, he will come out flashing. This is temporary invincibility, use it to your advantage and try to get past as many hard-to-kill enemies as possible. But watch out - it doesn't last for very long.
• Stages 31-36 are "secret" stages which can only be accessed if you defeat Dark Paccet (the boss of Stage 30) on your first try.
• If you complete the game (it doesn't matter if it ends at Stage 30 or 36), you cannot enter your name on the high score table...boo!