The TF2 hat is fashioned after the hat that Maxwell wears in the Scribblenauts games, and the game's official Twitter account showed the pre-order bonus in action earlier today with a tweet linking to the pic above.
The game is set for release Nov. 20. on Steam for $29.99. Scribblenauts Unlimited will also release in time for the Wii U's launch this weekend with in-game Nintendo characters. A 3DS version released yesterday does not include the Nintendo characters.
For more on the Wii U version, be sure to check out our recent feature, where we talked to developer 5th Cell about how the Wii U changed Scribblenauts.