In comparison to the normal game, these levels become intense and hard as nails. Not that the normal game becomes tricky towards to the end, but here they are relentless. Finishing them is one thing, but finding all the Star Medals without dying is your true way to completion. Don't worry if you can't finish one though, as you play these in any order you like and are therefore free to skip levels. I haven’t completed every challenge level just yet, due to the fact that they are this hard. Advanced and veteran players will certainly be entertained and pleased with a game that gives you more for being a completionist.

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Source: Nintendo World Report