On the Title Screen, wait a couple of seconds. Small multi colored stars and moons will then appear on the screen. Tilt the game boy left to move the stars and moons left, right to move them right, up to move them up, and down to move them down.
Hard mode
Collect all the Red Stars to unlock Hard Mode.
Invincibility
Set up a red bumper exactly vertical or horizontal with the bumper. Repeatedly roll into the bumper to become temporarily invincible. Use the blue glove power-up to get pushed in the air three times consecutively to become temporarily invincible. Enter a jumper, then jump out of it and into another jumper. Immediately jump out again into another jumper. Jump out once more time to become temporarily invincible.
Replay levels
Defeat King Dedede to replay any desired level.
Special mode
Collect all of the Red Stars in Hard Mode to unlock some secrets. The sky changes pink, there are Kirbies you can control in the opening scene, and a free-play mode will be available for mini-games.
Unlimited lives
When you start level 4-3, you will see four Waddle-Dees walking around in a circle. Flipped, they will turn into blue stars. Collect all four of them to earn a life. Repeat this as many times as needed.
Warp from 3-1 to 6-1
In 3-1 you have to go northeast from where you started to warp. To do this, jump the first bridge and get to the end. Go across the water to your right, and you will find a tree. He asks you if you want to warp to 6-1 from there.
Fun with the Title Screen...