This hack suprised me. I liked it quite a lot. The design choices overall were nicely executed.
A couple of minor complaints:
-The first level doesn't leave too good of a first impression. It's repetitive, tedious and not fun. A shame considering the 8 other levels are enjoyable.
-The style clash (YI, SMW, SMB, SMB2, SMB3) sometimes works, sometimes it doesn't. Having two types of Shy Guys, the YI and SMB2 ones, in the same level is an example of the latter. Would've been fine to use them in seperate levels.
-You only used a couple of enemy types, and I must say, most of the time I actually liked that choice. You tried to make the most of a limited section. My complaint is that some enemies are especially underused in some levels, only appearing once or twice. Could've done with focusing on what you already had and using them in a creative way.
With that nitpicking out of the way, change the first level and the hack has the potential to be a popular choice. Nice job.