Doc Slaughter and his array of appendages.
Doc Slaughter is an earth pony scientist who works for Red Eye. He is a high up member of Red Eye's scientific division and a rival of Doctor Glue.
Doc Slaughter along with Doctor Glue, Red Eye and Gizmo were originally residents of Stable 101. He survived Red Eye's slaughter of the stable's inhabitants and joined him. He was severely injured and lost his limbs and portions of his lower body at some point. His missing portions/limbs were replaced with a cyberpony body that gave him a metallic body with treads to move and a spiderlike array of robotic appendages that hold numerous tools, dissection implements etc.
Doc Slaughter along with Doctor Glue are competing scientists, working for Red Eye. Doc Slaughter specialises in cybernetics, he was tasked with improving the old and failing portions of an old dragons body. Doc Slaughter succeeded, creating the Cyberdragon who proved to be one of Red Eye's most formidable assets during the Enclave's assault on the surface.
Doc Slaughter was encountered in Red Eye's cathedral, commenting on Regina Grimfeathers strong physique and how he could make her better. She turned him down, much to his dissappointment, but later made the new cyberleg for the Albino Hellhound.
His fate afterwards is unknown, though he was likely killed by the Enclave like his colleague Doctor Glue or he escaped.
Doc Slaughter is mostly cybernetic, due to most of his body being damaged in an accident. He moves on treads and has an array of robotic appendages that help him with most of his activities.
Doc Slaughter is a highly skilled surgeon and an expert on cybernetics. he was able to convert a dragon into a cyborg and create a leg for a hellhound with ease.