Giant acorn
From Starfy Wiki
Giant Acorns are found in the Sogwood Forest. There are two types of Giant Acorns: Brown and Green. Brown Acorns float on the tops of Poison Ponds, allowing players to cross them without getting hurt. Green Acorns sit on the ground until the player uses a Star Spin to knock it back and into a wall. The force of the hit causes humungous bubbles to fall from the sky. The player can swim up and through the bubbles to reach areas that were previously unaccessable.