These new challenges are placed in Secret Chapters. If you didn't already find Secret Chapters, you will have to locate them first to access the new challenges. Note that there are two new challenges per World and that we are introducing a new difficulty: Ultra Hard.
We are also including 5 new Coop Challenges. They can be found at the Buddy Dome in the Peach Castle area. For more information about Coop Challenges, check out this article.
Do not hesitate to contact us if you have any questions about this new content.