"The last wave is here! FIGHT!"
So, by a large poll majority, the "Ponies VS. Changelings" wallpaper idea was chosen. Parody (a poor one) of the MVM Wallpaper. [link]
Rainbow Dash, Spike, Big Mac, Zecora, the Changelings, and MLP: FiM belong to Lauren Faust and Hasbro.
All characters portrayed and Team Fortress 2 belong to Valve.