Sea

Sea-1-IamTehShark.mp4

(video credit: IamTehShark)

Sea star movement [2904330985].mp4

Knock out all 14 zeostars with the EXP star. (Mallow is not guaranteed to learn Snowy later on when he needs it if you fail to hit all 14)

(video credit: kbz)

Level up:

Mario [7] - SP

Mallow [7] - SP

Mallow [8] - SP

Geno [8] - HP

Peach [10] - HP

Sea-2-IamTehShark.mp4

If you scored less than 4 flowers on Booster hill, go into the door above you and get the chest with the flower in it

(video credit: IamTehShark)

Sea-3-IamTehShark.mp4

Exit the cave
On the final screen, run into the first whirlpool without jumping, then enter the pipe on the ship

(video credit: IamTehShark)