Yeah, the taotie is one of four legendary creatures often called The Four Fiends. So with all the talk of sequels, you got at least three more to build the Great Wall universe. The Hundun, a formless creature of chaos with six legs, four wings, and no face, although it's also been described as a large sack; Qiongqi, a cross between a hedgehog and large tiger that flies with giant wings; and the Taowu, a shaggy beast with a human head and long boar-like tusks. It's clear the moviemakers just wanted to use the Taotie in name only to refer to the alien dogs that act like hive-mind insect swarms, but for the record the mythological Taotie are creatures with a giant ram's body, tiger’s teeth and human face and hands, although its eyes are hidden under his armpits and has a baby’s voice.
The Four Fiends are the evil counterparts for the Four Auspicious Beasts, one for each of the Four Courners of Heaven, aka the cardinal directions of East, West, North, South: the Blue Dragon, the Vermilion Bird, the White Tiger, and the Black Tortoise. I kept looking for ways that the movie might make the human characters stand-ins for one of the Auspicious Beasts in order to symbolize the mythological rivalry, but then I realized I was giving more thought to it than the filmmakers did so I stopped.
Disclosure: not Chinese, just a folklore enthusiast.
Disclosure II: not Chinese, but after living in Shanghai for five years, I've become *That Guy* who cringes every time every single person mispronounced Taotie. It should be "tao-tee-yay", but I'll forgive if you don't have a falling tone on the last syllable. I did look up "tao-t-a-i" that slant rhymes with "bow tie", and apparently "淘汰" could be read as "natural selection" or "elimination as in natural selection," so that fits!