This idea may have been used before by someone else, but just think of how easy that would be to totally disregard.
All you have to do is post a comic that someone else has done, and continue it into a series of five or less (including the original comic). However --
The comic you use must be chosen by using the random button at the top of the page. Just in case you happen to get a real dud on your first try, you may hit the random button up to five times, and use one of those five. It can't be one of yours, and it can't already be part of a series, so if you get one of those it won't count as one of your five choices. But if you do use a really crappy comic you will get extra points for taking on a greater challenge.
It sounds like fun to me! I hope it sounds like fun to you. I have already presented this idea to a carefully-chosen test audience, and here is the actual reaction:
I will judge this contest after one week or one-hundred entries, whichever comes first.
Legend, oh legend, the third wheel legend...always in the way.