Super legs of doom are a Vortian creation. They attach to the users brain and stubs where their legs should be, and work much like Earth's primitive prosthetics. Unlike prosthetics, they have guns, rocket boosters, can run really fast and jump really high. They also repair themselves when they are damaged.
The Super Legs of Doom were created by a Vortian Inventor when he lost his legs in a war. He didn't want to lose his favorite ability, walking, so he created legs that would be able to do anything. To avoid a repeat of when he lost his real legs, the inventor developed the ability of self repair. Because his arms always got tired carrying his weapons, the inventor added weapons to the legs. To escape danger, he added the ability to jump high and run fast. For air combat, the inventor added rocket boosters. The inventor eventually got an award for making the best artificial legs.