Challenge 21 is a One-Minute Challenge, divided into four rooms with 15 seconds per room. The rooms are as follows:
Room
Description
Notes
Room 1
This is an entirely underwater room. Kirby must defeat the four Blippers swimming through it to make the treasure chest appear to the right.
Room 2
This is a half-flooded room, with two rings of Point Stars to collect. Once they are all collected, the treasure chest will appear.
Room 3
This room's chest is guarded by a water geyser that will push Kirby up past the thin floors if he moves into it. The geyser can be blocked by a rainbow rope for easier access.
Room 4
This room's chest is locked away in a ceiling cache. To open it, Kirby will need to slip past the two Dethskullks on patrol to grab the key in the lower-right corner, then head up to the chest to obtain it.
Even if Kirby is K.O.'d after grabbing the chest, it will still count.