Here is an aspiring entry from the Robo-One competition in Japan the KHR-2 or "Layered X". The robot walks on 4 feet but can instantly transform into a robot walking on 2 feet. Further more a modified KHR-2 can also be attached too, kind of like a Mini-Me which sits on its shoulders and performs co-ordinated moves.
(Videos after the jump)

Cool Transformation

KHR-2 and Mini-Me