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. Note: This also allows the original levels to be replayed with time limits.

Collect all the Red Stars to unlock Hard Mode.

Defeat King Dedede to replay any desired level.

Complete the game once

Collect all 32 Red Stars

Remain idle at the title screen until stars and moons appear. Tilt the Game Boy Color to move them in the corresponding direction.

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.