In your own space, create your own challenge. Whatever your challenge is, and have fun with it! Leave a comment in this post saying you did it. Include a link to your post if you feel comfortable doing so.
Okay, I'm going to lay out a menu. Play as many items as you wish ...
1) Aspect a character. Aspecting means that you take an archetype or a canon character -- or even yourself -- and then change details one at a time until you have something different yet still recognizable. Racebending and genderbending are two popular examples. For instance, The Ursulan Cycle is genderbent Arthurian Cycle. The Blueshift Troupers features shapeshifting across racial, gender, ability, orientation, and other lines. Schrodinger's Heroes involves multiple dimensions so there are many "alter" versions of characters whose traits differ from the "core" ones -- and in fact the canon includes both a female and a male Morgan. Then you explore how those changes affect the character and plot.
2) Practice building from the core out. Explore Scott McCloud's Six Steps. Almost everything I create begins either with Idea/Purpose and moves to Form, or with Form and moves to Idea/Purpose. You can do this with writing individual stories or with large-scale worldbuilding. Make a plot, make a continent, make a language -- just build something from the core out. It's much more stable that way and I'd like to see more people do it. In writing fanfic, I phrase it "derive in, extrapolate out." That means look at canon and try to imagine how it got that way. With your explanation in mind, project forward to imagine how that would influence new stories. For example, "Little and Broken, But Still Good" explains why someone as powerful as Phil Coulson routinely uses underdog tactics to accomplish his goals.
3) Come play in my sandboxes! The Blueshift Troupers, Schrodinger's Heroes, and The Ursulan Cycle are all shared worlds. Honestly, Polychrome Heroics has pretty much turned into that, of which the Berettaflies thread has the most guest creator activity. If you want to write a crossover with your favorite fandom(s) then I recommend Schrodinger's Heroes, because it's designed to facilitate crossovers. The section on LOL_HEROES is whimsical lolcat imagery of the characters, featuring both the ones who are normally cats and the human ones transformed into cats.
4) Write a poem, fanfic or original. I have worksheets on how to write acrostic, ballad, and list poems, nature poems, and science fiction poems.
5) Create a piece of demifiction. That's a piece of nonfiction taken out of its original universe, whereupon it becomes fictional, but it's still not the usual kind of narrative story. For example, a newspaper article, advertisement, postcard, book excerpt, description of a television show, magazine cover, etc. Need more ideas? The Bingo Card Generator offers a list of demifiction prompts.
6) Make a bingo card. The Bingo Card Generator has dozens of prompt lists for all kinds of topics and even different media. Card sizes range from 1x1 to 7x7 with various features you can play with. Looking for moral support? allbingo is running Apocalypse Bingo in January and will do Valentines Day (both romantic and platonic) in February.
7) For artists, do a colortest. Take a simple sketch of a character or other item, then color it in several different ways. This lets you explore the effect of different palettes on a small scale before you do it on a large scale. Really nice for aspecting characters who have a very consistent dress mode in canon. Harry Potter fandom is famous for doing this with cross-house colors.
8) Explore character emotions. These examples are for art: 25 Essential Expressions, 25 Smiles, and Expression Intensity Chart. For writers, use this body language cheat sheet as inspiration for a vignette.
9) Our meta is so meta! Launch a discussion on any of the above topics, here or in your own blog.
If you post what you make to your own blog, please reply here with a link so that other folks can enjoy it. Have fun!