Essentially, someone wrote a game that allows you to play randomly generated Super Mario levels of arbitrary difficulty, and the contest was to write an AI that gets as far as possible on those levels, in real time. This is the winning entry.

(They actually ran two separate contests, but the videos of this agent were released around the time of the first contest, which I think would have discouraged new entrants for the second. Independently, the video went viral in Japan and picked up half a million views.)