DC Challenge was a 12 part maxi-series and a "round robin." between 11 artists and authors. A round robin is where one team creates a chapter of the comic, then pass the next chapter to another team.
In this case, each team had a different writer and illustrator, and the authors could NOT talk to each other about what they were doing. Each team was required to create what seemed to be an impossible cliffhanger situation, and it was up to the next team to provide some solution to the problem; the solution could be anything from the DC universe, including any character, item, concept, etc. The teams had to have some solution (nothing really impossible), which would be featured in the next issue. The covers proclaim "Can you solve it before we do?" The reader is invited to come up with his own solution, although it may not be the same one as the solution provided.The last issue was a collaboration between all the artists and authors, and proclaims "We solved it -- have you?" Well, have you?