Drive the Gyrocopter
Going along with the above trick, when you head down in the gyrocopter, try to keep your speed at 40 mph or less once you've hit the ground. If you're careful, you can drive the gyrocopter along the ground, and steer it left and right.

Warp From Seattle to Miami
Enter the little states course using the rocket pack. Fly either to Seattle or to Miami. Enter the white hanger (through the back) where it isn't quite shut. You will be warped to the opposite hanger.

Birdman Transformations
As I am sure that most players have noticed, there is a yellow star in every level of this game. If you touch them, you will become Birdman in level which you began, but you will start that level over. You can use any vehicle to get this star.
Beginner Class
This star is inside a rock in the shape of an arc (between ocean and the island).
Class A
The second star is in the center of Central Park, New York City in the Little States island.
Class B
On Ever-Frost Island, the star is located inside a cave from which a waterfall appears. There are two waterfalls -- take the smaller one on the right and follow the cave until you've reached the end. Change your viewpoint to top down and you'll see an underground cavern. Lower yourself slowly down and you'll find the star.
Pilot Class
Crescent Island's star is located in a cave along the ocean between the airport and the little village, and is located inside the rock face.

Refueling
To refuel your Gyrocopter or Rocketbelt on the Little States island, you can fly along the Northwest road from Cape Canaveral. You'll see what looks like a gas station on the left -- the sign is actually a Paradigm logo. Fly low and slow around the station until you hear a noise. You will then be refueled.
You can also get fuel in the little town near the nuclear plant. Just fly under the little station's roof and you'll have a full tank.

Night
In the first level, get the rocketbelt. Fly into the cave under the castle until you get to the gate. Right before you reach the gate, the game will pause and it will turn into night.

Wario's Head
While in Cannon Mode on the Little States island, aim for Mario's face on Mt. Rushmore. In the next view of the mountain, you'll notice that Mario's head is now that of Wario's!

Warp From San Francisco to New York
There is a green building in both of these cities with an entrance at the bottom. Fly through it, and you'll end up in the opposite city. (You have to fly through the right entrance to the building for this to work).