Also: this is a FUN ficathon. A ficafunathon. Funaficathing. Something like that. The sillier, the more carefree, the better! (Although, if you end up writing the Best Thing Ever, we'll love it, no matter what.)
If you are stumped, if you need any help, feel free to ask! The HP fandom (where the idea was taken) has an entire community devoted to these types of fics, found at perposterice. Check them out for inspiration.
Lastly, and OT: Happy Birthday to serenelystrange and ropo, icon maker extraordinaire! Hope you both have lovely days today!