Super Mario Bros.: The Mystery of Luigi is a ROM hack of Super Mario Bros. that parodies Transformers: Convoy no Nazo and is made by the same person that created Extra Mario Bros. Luigi is missing and was possibly kidnapped by a really big Bowser, and it's up to Mario to find and rescue him. It may be a relatively short hack, but it has very good presentation and a couple of new mechanics that make it very different from most SMB ROM hacks.
HappyLee abuses various glitches in this run to get the best ending where Luigi is rescued in record time.
Watch a resync of this run being played back on a real console.