Artist Mike Dietz, who worked as an animator on both Earthworm Jim and Earthworm Jim 2, has graciously responded to a number of fan requests by posting sketches and other development art from the two games to his blog.
There are some really groovy drawings showing a lot of ideas that made it into the games, and even more interestingly, a lot of ideas that didn’t. Take for example these cruel tricks designed for Earthworm Jim 2 that never made it into the game (thankfully—as if it wasn’t already hard enough!):

Or this amazing background detail for what presumably turned into the New Junk City level from the first game:

Be sure to check out all the fantastic Earthworm Jim images on Mike Dietz’s blog, Slappy Pictures.
Via Anonymous.