>Despite appearing very sluggish, Purugly will not be reluctant to attack if angered and can be quite fast.
Purugly is also based on a cat, and cats are generally very speedy. Its fat might be some kind of protection it got when it evolved, to improve its defences, considering how they arent too good. Its pokedex entries also say that it invades other Pokemons nests until it finds a comfortable one, so it would need to be quick to be able to chase the other Pokemon away. Perhaps it could run faster than a lot of Pokemon, but would get tired out easily, like how some people can run really fast, but not for long-distances, while others can run for a long time but arent very fast. Other than that, only Game Freak knows.