Jelly Boy is a platformer in which the player controls a pink blob with transformation abilities. In comparison to the SNES version, the Game Boy version has a different level design.
The gameplay mechanics are the same, though: the blob has the standard abilities to jump and punch enemies. Collecting power-ups transform him into other forms with different abilities, e.g. a balloon which allows him to float. Other collectibles are music notes (those are lost after being hit by an enemy; without any notes this results in death) and fruit which eventually reward an extra life. The game features six worlds with eight levels each; every level has to be completed within a time limit.