Did you complete all of the secret objectives in Captain Toad: Treasure Tracker? Mummy-Me Maze Forever is your reward, the most difficult level in the game.
I completed this level after about 15 tries over a few days. I thought I would share my thoughts and strategies along with some information about the floor composition, because I haven’t seen much analysis online yet. Lots of people find this level to be frustrating, but I thought it was a lot of fun to work out. There are several YouTube videos showing playthroughs to completion though, so those might also help you out if you’re stuck.