Tuduo.com has a video of a very hard custom level of Super Mario. It's a couple super difficult levels, with all kinds of tricks and and timining problems that make finishing it very impressive. Nintendorks (aka "RubixsQube") apparently added the audio however. The video is interesting but, parental warning, the audio is filled with profanity. Funny profanity, but seriously, lots of profanity (adults only please).