Yeah so I actually did a lot of small things during the 72 hour Jam instead of one big thing.
First, I started (what will be) a weekly drawing prompt on /r/tf2 that will be designed to teach others how to improve their artwork.
Then I drew a doofy-looking Saxton Hale:
after that I drew a BLU snowy Sniper using Crayola crayons:
And finally I did a study to see how Valve's artists handled drawing the eyes of various TF2 characters: