Excellent. I had a few gripes, though...
-In Uphill Struggle, horizontal scrolling was enabled in the bonus room, and the pipe kills you when you come out at the end.
-The second overworld has green water for ground. It looks... really weird.
-The second overworld's music sucks. Period.
Putrid Puddle was a little too bland.
-The Great Boo fight was hard. Really hard. Very fun and unique, but it calls for serious savestate abuse.
-You needed to be big to get past the second flying hammer bro in Pipeline. I tried to do it as small Mario, but you can't kill it without hitting one of his hammers or falling into the pit.
-What's the music you used in Pipeline, it's REALLY familiar, but I can't put my finger on it...
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Mario's Nightmare Thread