Piranha Plants on Ice
From the Super Mario Wiki
Piranha Plants on Ice, or Layer-Cake Desert-, is a secret course hidden in Layer-Cake Desert of New Super Mario Bros. U. Although this is a Layer-Cake Desert level, the course is actually situated on a block of ice in Frosted Glacier to the right of the cake structure. To reveal this level, the player must locate the secret exit in Spike's Spouting Sands. Finishing this level will unlock a shortcut to Soda Jungle (which skips Frosted Glacier on the map).
All of the foreground is slippery ice. In some spots, Fire Piranha Plants are placed where they are able to melt the bottom part of the ice blocks, so the ice blocks can either fall on the player, or cause them to miss a jump and fall into the pit.
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