Serpents are known as imperfect dragons and symbols of Man, as explained in the desc. of the silver serpent rings.
We know of Kaarthe and Frampt as Serpents. Therefore making them imperfect Dragons and symbols of Man.
But there is one other being we know. A creation made in Drangleic. An amalgamation of Dragon and Man. Who came out imperfect...
Shanalotte. She is a "serpent" or an imperfect dragon. Acting as a symbol for Man and assisting the Bearer of the Curse to ascend the throne and therefore link or snuff out the flame.
Honestly. This kinda popped in my head and I thought it was a very interesting idea. It makes some sense and would make Shanalotte a lotte more interesting xD.