Modded levels of Super Mario World set to automatically "play themselves" without any outside input. Pretty damn cool. Then people started adding in music and making the sound effects in the game play along to the song. Things were starting to go well past crazy into scary/ obsession territory.
Well, how about two levels playing along to the same song at the same time! Not only that, but each level actually builds on the other, often seeming to interact. Like something on a Nintendo DS, the dual screens often meld into one, forming pictures and words as they speed along together. All of this is set to another Haruhi song, this time it's the character song "Yuki, Muon, Madobe Nite."