Turn into a nearly feral lamia in the book Dark Assassin. He stands upright like a human and his face look much more human than lamia. His eyes and nose were his own too. But his mouth is wider. He is known to have transformed into this form only twice. Once in Dark Assassin and again in Brother Wulf.
Here is an extract from Dark Assassin:
"I opened my eyes and saw that the inside of my grave was glowing with a red light. I could pick out every detail of my surroundings: tiny insects weaving patterns on the soil as they scuttled to and fro; worms moving deeper within it, creating labyrinthine tunnels. Above, the clouds still raced eastwards, blown in by the wind from the sea. But I could see through those clouds to each of the myriad stars beyond. They glowed like eyes in the darkness. There were smells too; odours sharper than I’d ever sensed before: the smell of grass, leaves and the distant sea. But even stronger than that was the sweet odour of blood … though it wasn’t my blood. For some reason I couldn’t smell that, although I must have bled from my injuries. The blood I smelled was the blood of my enemies. It was strangely attractive. It seemed to be calling to me. I had no doubt now: I had changed into a lamia. It was time to take what I needed. It seemed I’d been lying in the same place for far too long, so I sat up and stretched my limbs, freeing myself from the ropes. All at once I felt a series of irritating itches, and plucked away the sharp stakes that had been driven through my flesh as if they were merely thorns. I got to my knees and then my feet, luxuriating in the new sense of freedom. Why had I stayed in this pit for so long? Why had I delayed? I was strong and full of energy now. I also felt a terrible thirst that only one thing could assuage: the blood of my enemies. I bounded up onto the grass and began to move towards that delicious scent; towards the fire where the four figures stood. Two ran away at the very sight of me; the third charged towards me, jabbing at me with a pointed stick. I grabbed him by the shoulder, shook him, then flung him aside, watching his body turn over and over in the air before crashing into the ground. The fourth, the larger one, was jabbering nonsense and gesturing with his hands. I reached out and ripped away the thin metal that clad his body. Then I drank his blood while he screamed in agony. Later, still thirsty, I returned to the assassin. His neck was broken and his blood was almost cold, pooled by gravity within his body. I drank just a mouthful, then spat it out. Next I searched for the other two, who were still fleeing. I could have caught them, but the sun was rising and my need was diminishing. Instead I walked towards the lake and knelt beside it, my mind empty. I stared at my reflection in the surface of the water. What I saw was not quite what I’d expected. There were two types of lamia witch: the domestic and the feral. The former was almost totally human in appearance, whereas the wild version scuttled around on all fours, with sharp claws and teeth, and green and yellow scales. In addition there were feral vaengir, which could fly. I certainly didn’t have wings, but my reflection told me that my form lay somewhere between the feral and the domestic. I could walk upright, and as I gazed at my reflection, I saw that my face was still much more human than lamian. It was elongated and partly covered in green scales, but my eyes and nose were my own. My mouth was wider, and within it were two rows of sharp teeth almost as pointy as Grimalkin’s. I looked down at my hands. They were human in shape, but partly scaled, with long, sharp nails. A domestic lamia retains its human shape because of close association with people; in isolation it slowly shifts towards the feral form – a change that can take weeks. My transformation had taken less than an hour … So, I reflected, I was different; something new; the result of both my father’s and my mother’s blood fusing within my veins. Was the change permanent? I wondered. Would I stay like this? All at once I felt utterly weary, my mind sluggish, so I lay down by the water, letting all my concerns drift away. I think I slept for a while. When I awoke, I looked at my reflection again and saw that I had returned to my human shape."