Chapter 5-3 ("The Gap of Crag") is a linear platforming/puzzle stage in the Floro Caverns. You don't "solve" it like a riddle—you traverse it using dimension-flipping and partner skills.
Search "Super Paper Mario Chapter 5-3 walkthrough" on YouTube for a 2-minute visual guide. No shame—some flip puzzles are deliberately obtuse.
Keep flipping. The next dimension always has a path.