From the Super Mario Wiki
Firefall Cliffs, or Peach's Castle-4, is the secret fourth course of Peach's Castle in New Super Mario Bros. U. It is unlocked via the secret exit of Meteor Moat, and its own completion unlocks Red-Hot Elevator Ride.
This course is an autoscrolling course that involves climbing walls and dodging meteors. Meteors fall from certain points, and the player must climb on certain parts of the area to make their way through.
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