Ferenks are Free Magic elementals of stone and mud. They have a body of mud and rock, and they have a mouth of pure darkness with a tongue of silver fire. They are not particularly dangerous, being scavengers and, according to the Disreputable Dog, “all show and blunder.” The Dog also says that when the Charter was made, Ferenks became “nothing more than stone and mud”. This suggests that most Free Magic elementals dissipated into their respective elements when the Charter came into existence.
Lirael, Sam and the Disreputable Dog encounter a Ferenk at the top of the Long Cliffs. Arrows and strong Charter Magic didn’t appear to have much effect against it.