VGFacts

The sixth and final level is called "Hyper Zone", which is a reference to one of HAL's earlier games called HyperZone. This game also has levels named "Ripple Field" and "Grass Land", which were also level names in HyperZone.



http://kirby.wikia.com/wiki/Grass_Land
http://kirby.wikia.com/wiki/Ripple_Field
http://kirby.wikia.com/wiki/Hyper_Zone

and for proof of the levels from HyperZone;
http://youtu.be/1tM8EjFIV1k?t=8m38s - Grass Land
http://youtu.be/1tM8EjFIV1k?t=11m56s - Ripple Field
http://youtu.be/1tM8EjFIV1k?t=21m35s - Hyper Zone