I cannot provide videos for my 2 suggestions (cuz I succ at gamee loll) but I believe my 2 suggestions would be fun and challenging

all suits: get all the suits (frog, tanuki, hammer) in the player inventory time starts on pushing start and ends on collecting the final suit needed

all items: collect all 14 obtainable items in the game that can go in player inventory time starts on pushing start and ends on getting the final item you need to complete the run

secret mushroom house exit%

Awesome!

Last stage IL