Hidden Island 11 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 abandoned mining equipment, like pulleys.
Like most other Hidden Islands, Hidden Island 11 is a short stage which can be finished in less than a minute. While the stage does not focus on a certain gimmick, the enemies are usually positioned in clusters or formations that make it difficult to go up and down without ramming defenselessly into them. It is thus advised that the player surveys an area as they move into it.
An underwater-themed stage, Hidden Island 11 has a few underwater sections, though they have no Air Bubbles, leaving the player at greater risk of drowning. The stage also borrows the wooden arm gimmick from Coral Cave that will take the character to another elevation in the stage upon running into it. In addition, there are lesser gimmicks like Rainbow Rings.
At the beginning, follow the path into the water, but watch out for fish Badniks on the bottom. Once out of the pool (watch out for crab Badniks at the ledge), follows the path to the wooden arms. As the player scales platforms with this gimmick, stay close to it and boost through the Badniks up front. Use then the Rainbow Rings at the top (watch out for bat Badniks above) and break through the coral platform to the right with the crab Badniks below.
As the player scales the follows steps on the path (with bat Badniks coming swooping in), continue into the water, but watch out for the fish Badniks. Follow the path out of the pool and the characters will find a Treasure Chest.