Defeating the Red Baron
You can only defeat the Red Baron on level 25. Cheat mode
Successfully complete the game to unlock a special option for cheats in the "Goodies" screen. You can become invincible, get a booster, and have unlimited rockets and bombs. When you have booster and bombs both activated, hold [Boos, drop a bomb, and release [Boos. Your bomb will travel faster than a rocket, and will go long distances.

The trick to defeating him is not to shoot him down. Allow the Red Baron to get behind you. He is usually the second bogey you encounter. Go into vertical climb, then when you hit the ceiling, go into a nose dive (the more vertical the better). The Red Baron will follow. Immediately before you hit the ground, pull up. The Red Baron, being under-powered, will crash ending the game.

Fly over the clouds
Climb until your plane cannot fly higher. Turn off the engine, then quickly pull up on the stick slightly.

Land on water
The game will allow you to land on water.