### It walks with its three legs.

The 5th Edition *Monster Manual* gives an image of a Otyugh running on pg. 8:

[![enter image description here][2]][2]


Also on page 8, we see the [rules for monster speed](https://www.dndbeyond.com/sources/mm/introduction#Speed):

>All creatures have a walking speed, simply called the monster’s speed. Creatures that have no form of ground-based locomotion have a walking speed of 0 feet.

We have an image of an Otyugh running and it has a speed of 30 feet, which the rules explicitly call its walking speed. So it walks with three legs. 



  [1]: https://i.sstatic.net/Pk5B6.png
  [2]: https://i.sstatic.net/0q588.png