Kirby 64: The Crystal Shards: Part 13: Aqua Star 4 (All 3 Shards)
3This last regular level of Aqua Star takes place entirely underwater, and it comes with that ethereal ruins music that was first heard in Rock Star 2.
This game treats underwater controls completely different. Kirby can still use almost all of his basic moves besides floating, and he can still use any of his Copy Abilities underwater, including anything that involves Fire.
On top of all of this, it seems that Kirby is once again fine with swimming without a snorkel mask. Not sure what is of this for the rest of his gang. Maybe Ribbon has fairy magic that lets them all breathe underwater?
A good chunk of this level involves bracing yourself against the different underwater currents that can carry you into different directions, including some hazards you'll want to dodge.
The only time you'll see the whole gang on dry land is at the very end when you do your Picnic Jump.