Jelly Boy is a pink, amorphous blob that usually takes the form of a pudgy humanoid that is currently attempting to escape a shady toy factory he wakes up in. To do so, he needs a series of objects before the elevator operator will allow him to take the elevator to the roof and escape the compound. The objects can be found in six separate worlds and Jelly Boy must explore all of them to earn his freedom.
As well as jumping, attacking (using a fist that extends out of his stomach) and ducking (which literally turns him into a duck), Jelly Boy is able to employ various abilities by collecting power-ups that resemble him. These power-ups will transform him into a new shape which the player can use to progress or find treasure.
A partial list of these special abilities include:
Hammer - Jelly Boy's upper body changes into that of a hammer, which allows him to smash through specific walls to progress.
Balloon - Jelly Boy inflates, allowing him to rise and fall through the air. He is also able to fire pellets to attack airborne enemies.
Submarine - Jelly Boy becomes a Submarine, able to travel through water and shoot torpedoes.
Ball - Jelly Boy becomes a sphere, allowing greater jumping power but harder-to-control movement in general.
Brick - Jelly Boy becomes a brick. All he can do is tip over and lie there until the power-up is canceled.
As well as reaching the end of the stage before the timer runs out, Jelly Boy also needs to collect a hidden puzzle piece on each one. These pieces will unlock that world's boss which needs to be defeated for the all-important World Item needed for the elevator. Also hidden on one of the stages in each world is a key. This key is vital as it is required to open up the next world, which the player can choose in any order (though the Toy World is always the default first world). He can also collect musical notes, which have a similar protective property to Sonic's rings: If Jelly Boy is hit, he will lose all his notes instead of dying.
Helping Jelly Boy is Helpy Block, a block that doesn't mind being smacked around so it can be positioned to assist Jelly Boy get higher up. Also helping, in his own way, is Harry the Dog, who does nothing but bark at enemies ineffectually and can be punched for the sheer cruelty factor.
The game was never released outside of Europe. It is available on SNES and Gameboy. A Genesis port was planned, but canceled.