Smart Ball ("Jerry Boy" in Japan) is a platformer in which the player controls Jerry, a young man destined to be married to Princess Emi but is instead transformed by his envious brother Tom just before the wedding. Using his new gelatin form, Jerry must return to stop his brother from marrying his bride in his stead and find a way to turn back to normal.
The player, as Jerry, can use his amorphous form to attack enemies and traverse the stages. Jerry can stick to walls to an extent as well as stretch out his body to fit through narrow openings and attack. He can also collect and throw items he finds across the stage, such as balls. The levels are presented as a filmstrip and levels can be replayed by rolling back the filmstrip.
The US version of the game removed all the story elements, including everything to do with Jerry, Tom and Emi. Smart Ball had a planned sequel ("Jerry Boy 2"), but it was cancelled during development. The game is not to be mistaken for the SNES game Jelly Boy from Probe Software.
The game is also remarkable for being the first game legendary video game music composer Akira Yamaoka, the lead composer for the Silent Hill games (among others), ever worked on.