Technically this isn't what a Yithian looks like, it's what a Yithian possessing the body of a pre-human (and conically shaped) Earth species looks like. And also sounds like. And that look/sound is strangely haunting and substantially creepy.
The Great Race of the Yith made their first appearance in H.P. Lovecraft's "The Shadow Out of Time" where he described them as:
The Great Race’s members were immense rugose cones ten feet high, and with head and other organs attached to foot-thick, distensible limbs spreading from the apexes. They spoke by the clicking or scraping of huge paws or claws attached to the end of two of their four limbs, and walked by the expansion and contraction of a viscous layer attached to their vast ten-foot bases.
P.S. Is it just me or does this video make the Yithians look like a typical Doctor Who alien?