When Kirby defeats a boss (excluding King Dedede and Dark Matter), the boss fight becomes inaccessible outside of the Boss Endurance sub-game. The door that originally led to the battle still takes Kirby to the boss's area, but now the player must play a sub-game instead. In it, stars and obstacles come at the hero in different patterns, depending on the boss. He must collect all 14 stars while dodging or defeating the projectiles. Kirby can also bring Copy Abilities and Animal Friends to assist him. If he succeeds, the word "PERFECT!" appears on-screen and the hero receives a 1UP. If he is hit, the game ends immediately.
When Kirby is finished with the sub-game, he steps back into the stage selection area and the door locks behind him. The player must complete a stage or reset the game to play again. Clearing all six of these is required to earn 6% toward the save file's completion.
When the player completes his/her save file 100%, Bonus Chance is unlocked from the main menu. Simply referred to here as Bonus, it is a marathon of the six stages, which ends by tallying up Kirby's acquired stars. He is then given a score based on his collection.
- In Grass Land, Whispy Woods spits stars and apples. The stars bounce off the ground and fly through the air while the apples roll.
- In Big Forest, stars and Nellys move across the screen horizontally from both directions.
- In Ripple Field, the underwater passage scrolls to the right automatically. Stars and Gordos are scattered throughout, and Kirby must weave through the enemies.
- In Iceberg, stars and icicles fall from the top of the screen at varying speeds. They bounce slightly when they hit the ground, giving Kirby a slightly longer chance to touch them.
- In Red Canyon, Mr. Shine & Mr. Bright move about. Mr. Bright floats back and forth overhead, dropping sun beam attacks and stars. Mr. Shine rolls and jumps back and forth along the ground in an attempt to hit Kirby.
- In Cloudy Park, stars and Co-Krackos fly upward from the cloudy floor and quickly drop back into it.
- Ripple Field's Bonus Chance is the only one in which neither a boss nor a boss's projectile serves as an obstacle.