Stone Shaping Serpent

After generations of breeding, eventually the Yuan-ti were able to create giant serpents that could burrow through stone like they could through sand. These Stone Shaping Serpents provided many uses for the Yuan-ti, giving them the ability to make many underground tunnels to connect their settlements to each other, or to the many slave pits that they kept throughout their country of Oshal. Many also believe that these Serpents, due to their sheer size and speed, are also used to raid smaller villages in Knaeva, Alderhardt and the The Ithryl Woods, allowing them to burrow underground undetected at ludicrous speeds, and capture slaves before anyone is capable of realising what had transpired.
As previously stated, the Stone Shaping Serpents are extremely large, able to have full squadrons of Yuan-ti on their back as they travel underground, and are still capable of carrying that squadron as well as a dozen slaves as they return. The Serpents have thick, callous scales on their back, and two ridges of protruding scales along their back, aiding their stone shaping abilities.