After analyzing the HUD and collectibles, I think the rules could be "starting from a new file, complete every objective in every level (getting a Gold medal) inculding normal platforming levels, remix levels, multiplayer levels and knitted Knight trials".
For 1 player, you are allowed to bring a friend only After completing a level when you're about to enter in a MP level, and before entering in another level he must log out from the team.
That's just an idea that I had, I hope you enjoy It
For objectives I mean all Dream spheres, all cosmetics found in levels, acing the level, getting a Gold medal for points. For challenge 16 the Ripsnorter, a Gold medal + 15 spheres too.
For Gold medal, I mean the Yellow decoration that appears at the end of the level on the level's icon
The problem is you need 26050 bells for 152 buyable items which takes like 3 hours
Other info
1P 305 Dreamer Orbs 1P 131 Collectable Prize Bubble
2P 325 Dreamer Orbs 2P 227 Collectable Prize Bubble
You do not need to do 2p levels to get more buyable costumes you get all of them from 1p 1P 80 Total Levels 2P 10 2P Only Levels
So a run takes about 11 hours https://www.youtube.com/live/E6MS2uEBiE0?feature=share
