Don't know if we want to do any kind of prizes? Perhaps someone else could organize prizes, though if we don't care about that, I could do something like keep a tally of the longest streaks or at the end of each challenge give out some "bragging-rights" awards for the person who completed it the most number of times, had the most creative/impressive way of completing it, etc.
If you read Tek's posts, he has ideas for prizes, and can organize it :)
Bragging rights also in the form of a leaderboard stuck into the Challenges splash banner maybe?
I can help too. I already made few Event-like challenges on other site, even with prizes, so I think it could work here. From personal experience, month didn't work on the other site well and sometimes I had to extend the deadline, but if I remember correctly, here on PokeCommunity month was standart and worked pretty well :D
Also, on other note, what happened to Necrum?
The more help the better! Brainstorm here :)
Necrum became busy and stepped down from being a moderator, as happens to many over time. So no blue mod for now! But I can help you with most things that need mod buttons clicking~
Sometimes we could do "Theme Challenges", something like this: https://www.pokecommunity.com/showthread.php?t=348376
Where you built up a theme based team over 1-2 weeks (ofc with mons you obtain after you signed up for the Theme Challenge) and beat the E4 in order to get the reward. This challenge says it's post-game, so maybe we should restrict these Theme things to games where you've already beaten the champion, otherwise it would be more like a normal challenge playthrough, right? The reward could be to get your name on the Leaderboard for those weeks/months, with the first one to complete the Theme Challenge as the top spot and so on.
Other times we could do "Mini-Challenges" more like the Stadium Arcadium: https://www.pokecommunity.com/showthread.php?t=331904
and have plenty of mini-challenges that you can complete for points and if you reach a certain number of points you can claim a prize pokémon and the challengers with the most points get onto the leaderboard :D We could even organize the prize pokémon in different categories depending on different amount of points reached, maybe.