Weegee, I really liked the Shroom City level. It was very well-presented, and transitioned nicely into a weird puzzle.
I will agree that the the P-switch ice-platforming was a little annoying, though, and probably the weakest part. But I don't think you really need to change anything.
So far I've made three Marios:
A ghost house with some tricks: 95FE-0000-0033-26BB
A Bob-omb-themed airship: CFAE-0000-003E-E9A1
A sort of puzzle-y level using an enemy gimmick: BDFF-0000-0042-F6EE