Densetsu no Stafy 4 is the fourth game in the Stafy series of games. In it, you play as a starfish prince called Stafy, as well as his sister, Stapi. It's up to the pair to help the princess of the Ami Kingdom, who has had a valuable treasure stolen by an evil snake.
As Stafy, you must swim, spin attack, glide and dash through a series of puzzling levels, collecting star orbs which both replenish your health and function as the game's currency. As you progress through the game, you'll unlock new moves for Stafy, as well as the ability to play as Stapi, who has her own unique moves such as wall jumping and crawling. In addition to this, you'll also be able to ride animal friends such as an angler fish, a seahorse, a pig that throws sausages, and more.
Most of the levels have the objective of collecting an object for a character, or destroying some items or enemies strewn throughout the levels. The fourth level of each stage features a boss that you must defeat to progress to the next world. Players travel between worlds via a lobster that has an obsession with roses. Stafy will be riding a rose, and you must touch the touch screen with the stylus to make Stafi travel in a straight line to that destination. This must be done in as few moves as possible, as well as without being hurt.
The game also features a variety of different costumes that players can unlock. Most of these costumes are based on fan designs - a template of Stafy was available before the game came out so that players could design their own costumes for Stafy and Stapi to wear. Some of the costumes also react if you blow into the microphone.