From the Super Mario Wiki
Seesaw Bridge, or Soda Jungle-6, is the sixth course of Soda Jungle in New Super Mario Bros. U, located outside the Haunted sub-area of Soda Jungle. It is unlocked via completion of Painted Swampland or Deepsea Ruins, or via secret exit in Bridge over Poisoned Waters and its own completion unlocks Iggy's Volcanic Castle.
This level takes place in a forest area covered with poison and some of the platforms are seesaws. The seesaws tilt up and down, and some of the seesaws even go in a full circle.
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