Alongside Flatman, I was asked to make a villain of the Legion of Superheroes who could also flatten himself. Ron-Karr. Thankfully, working out the problem for one meant I had it worked out for both.
So, the flat form is made the same way. Using some type of crafting cloth I picked up from the store.

Since he only flattens, I just traced the Karnak body so he'd be about the same size. Glued two sides together with foil in the middle so it could pose a little. Again, I'm not much of an artist. Head was a random cast. Possibly from AngelForge. Had it for ages. Full repaint, and all done!