Difficulty bumped to Standard: Hard due primarily to Bowser's Castle. While the author encourages save-state use in it, I found that I was instead able to fly over and skip everything up to the final boss.
The invisible maze (which I also flew over) and some blind jumps in the final world also made it difficult in an unpleasant way. The secret exit in Ice World 2 was uncharacteristically difficult. Lastly, the knockback mechanic frustrated me, but I guess that's the price to be paid for being able to take so many hits.
Aside from that, the hack was pretty fun and not too hard.