Anything graphic is out of the question for me (with the exception of making a comic strip if visual shinyness isn't taken into account to elect the winner). You know you're only getting strawmen from me. So I'd say either drawing or writing. Writing has plenty of possibilities: short story, essay, describe a character/creature/location/etc. (existing or invented). It could be coming up with the best suggestions of stuff to put up in Britt's shop (although it doesn't exist yet). Or the best ridiculous nickname for Teyn. Or a family name for Saehral. Or how X character would do Y in real life.
Or it could be a quiz; contestants must answer questions about the comics in real time, we just need someone to come up with questions and "host" the quiz. I've seen that on a band's forum and it was a lot of fun.
As for rewards, maybe we could require an entry fee (something like 5$ per contestant with unlimited submissions) that would be sent to Britt and serve as a collective donation towards getting an update or two. As if that weren't good enough, the winner could have some kind of cameo in that comic or get a simple commission, something similar to vote incentives that isn't too long to draw (all of this depends a lot on Britt's time and opinion on these matters).
As a matter of fact, if that still stands:
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