Monopod

Only one known land animal and no ocean creatures are known to be naturally Unipedal. The Springtails (Collembola) group of arthropod (not insects) use hexapedal motion regularly. But when a quick escape is required, it will launch into unipedal motion using it tail.
Real mechanical devices (robots and hopping machines) have been created that use unipedal motion.
Other than these rare cases, it is expected that the monopod tag will be applied to aliens, supernaturals, mutants, biroids, fictional robots, fictional machines, or other fictional creatures. Anything that is injured or augmented from its original state and must learn unipedal motion, does not count. However any injured or augmented that had a preexisting instinct for unipedal motion does count.