We may not all have access to a 3D printer, but if we did, we would definitely recreate these awesome Mario Kart inspired RC Koopa shells.
Designed by architect Michael Curry, all you need to have to make your own team of Koopa Shells is a knife, a soldering iron, parts from an RC car, and the aforementioned 3D printer (Curry used his Makertbot Cupcake CNC paired with an MK5 Extruder print head).
If you're up for the challenge, instructions are provided on Curry's Thingiverse page, including video of the Koopa shells in action.
http://www.thingiverse.com/thing:10526