From the Super Mario Wiki
Fliprus Lake, or Frosted Glacier, is the secret course of Frosted Glacier in New Super Mario Bros. U. It is accessed via the secret exit of Swaying Ghost House, and its own completion reveals a Spine Coaster that rides to Rock-Candy Mines and allows access to Fuzzy Clifftop.
In this level, Mario and company must contend with several snowball-tossing Flipruses. Throughout the course, there are many floating crates in the lake that can be used as platforms. Most parts of the level have slippery ice ground and River Piranha Plants.
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