If you want to look at it that way, you're better off discussing "tier lists" or whatever. The game is "balanced" such that, were Stephen Hawking a special guest character, he'd be able to go toe to toe (or wheel to toe) with the grizzly bear, giant egyptian mecha-chicken and stuff. Jacks are made from papier mache anyway.
In Japan, the walls are all made of paper. Maybe it's shiny paper so you thought it was metal. Anyway...
http://uk.youtube.com/watch?v=EWw1zxFN-lw&feature=related
Papier mache.