Hidden Island 4 shares Coral Cave's design. The island is a cyan grotto filled with crystalline coral forming purple surfaces, white paths, intertwining crystal- and coral bridges, and pristine pillars. The bottom of the grotto is partially flooded. Embedded in the ground are colorful gems that constantly twinkle from the light columns penetrating the ceiling. Decorating the surfaces are various colorful coral clusters and crystals. Other features include clean waterfalls and abandoned mining equipment, like pulleys.
Hidden Island 4 was visited by Sonic, Tails, Blaze and Marine in their search for clues on how to access Pirates' Island. There, the heroes found a marker with a symbol on it that tells how to unlock the door to Pirates' Island.
Like most other Hidden Islands, Hidden Island 4 is a short stage which can be finished in less than a minute. However, it does not focus on a certain gameplay style or gimmick.
This stage borrows many exclusive gimmicks from Coral Cave. These include a wooden arm that will take the characters to another elevation in the stage upon running into it, and gigantic shards of green crystal which launch the characters in the direction perpendicular to the surface touched. The latter enables Trick Actions upon being launched. Finally, there are rocks suspended on the ceiling with coral which can crush the characters should they land on them. Rocks held up by red coral can be knocked loose with attacks to the coral, while rocks held up by green coral fall down on their own. Other gimmicks include Winding Ropes and Grind Rails.
At the beginning, go down the path until the characters reach a rock held up by red coral. Break this rock free and continue forward. As they follow the path, the player will be launched up to a rock that will fall down. Dodge left or right with a Hop Jump/Axel Tornado to avoid it. Cross then a bottomless pit with floating platforms while avoiding another falling rock and continue down the path to a red coral platform. Break through it and bounce to the right on the green crystal below.
Follow the path the characters land on until they end up in a recess with two falling rocks above. First dodge the one on the right and then quickly climb on top of it to dodge the one on the left. Go then to the right to reach the Treasure Chest.