I've created a very basic Wily Werewolf wallpaper that can be used for both Desktop as well as Login screen wallpaper. Refer to UbuntuHandbook's article on how to change the login / lock screen. Enjoy:

Wily Werewolf Wallpaper
Wily Werewolf Wallpaper

(Right click and download image)

Source: The wallpaper consist of two images, the background is from OMG! Ubuntu! and the Wily Werewolf is from Ubuntu Artwork