Our arrival on Pandaria is the first time we've encountered a race like the mogu. Not only have they displayed an alien and sinister form of magic that can warp flesh and impart life to inanimate objects (twisting and recombining souls in the process) but they've created at least two races to serve them. While we still don't know the origins of the pandaren (were they always there, were they created or twisted by the mogu, did their ancestors also stumble into the Vale of Eternal Blossoms) or how they ended up as slaves to the mogu, the grummle and saurok peoples and their origins are known to the Lorewalkers and can be found on shrines and in books throughout Pandaria.
What's fascinating to me is how the origins of these races demonstrate not only their own natures, but those of their creators. The mogu made the saurok as a caste of slave soldiers, yet failed to conceive of the notion that making a race of bellicose reptiles and arming them could possibly backfire on them. When the saurok eventually rebelled, the mogu were forced to destroy them by the scores, wiping out every saurok stationed in the Vale of Eternal Blossoms, but in the end the saurok survived and their war against their creators weakened the mogu.
Even more interestingly, the mogu created the grummles as a wide ranging servitor race, demanding that they toil as conveyors of goods and serve as observant spies for their masters, yet never bothered to explain to the grummles exactly what spying entailed and who they should be watchful for, believing these things to be self evident. The creation of the grummles reveals that the mogu are incapable of understanding outlooks that are not their own, and automatically assume that their way of looking at the world is the only way of doing so.