When I saw the theme yesterday, I was somewhat disappointed. Having the player be the antagonist in some way just isn’t inspiring to me. And I was looking forward to making some sort of physics or abstract-puzzle game, rather than a character/story-based game.
Beforehand, I did think of a mechanic for the “You are the Villain” theme. But when it came to premise or objective, I was empty-handed.
But it’s okay! I found a satisfying premise!

Current version: https://dl.dropbox.com/u/107314069/LD25/v0.1/index.htm
A bunch of kids (the red guys) have been playing among themselves… but none of them wants to be the villain in their make-believe games.
You, a grown-up, enter stage left. How fortuitous! The kids quickly recruit you, before running off to hide. (It’s like when they say, “tag, you’re it!”)
YOUR GOAL: You have Important Business to attend to. Get past the kids’ make-believe playground (the black area), with all your Official Grown-Up Items intact and ready to deliver to your Big Important Boss (who will be somewhere on the right).
To do (in this order):
1. HIGH PRIORITY: flesh out the gameplay
The vague idea involves having the kids repeatedly insist that the player chase them. If the player ignores them and simply goes rightward towards the goal, then the kids will sneak up and steal the player’s Official Grown-Up Items. (Then, if the player tries to approach the Big Important Boss, he’ll be turned away.)
Also, the gameplay should actually be affected by the grown-up becoming the villain. He shouldn’t simply be the “victim” of the kids’ mischief – that is not very villain-y!
2. Give the kids behaviors that implement the gameplay (they already have rudimentary ones)
3. Add the “Big Important Boss” and the items that the player must carry across the screen
4. Fix miscellaneous things in the code (e.g. display the people in the correct order, clean up animation code, etc)
5. Add title screen, instructions, ending(s), etc. (Get a better name!)
6. If time: tweak movement parameters, refine art
Art

Hahaha.
I’ll probably change those weird wings and claws. I want to give him fangs, too. But this is good enough for now.
Anyway, I’m having fun. I’m really pleased with the code, even though it’s crude and inefficient – it’s really easy to make the characters run around in the manner I want them to. And I’m glad that I got past the theme.
OK, back to the villain-izing!