Could he be a puppet similar to Sasori with Madara's heart? Not exactly similar, but more durable and flexible, made out of zetsu material? A puppet almost close to being human?
We know he had both. After extracting tailed beasts, he stored the corpses of the jinchuriki and also he had access to Kabuto's edo versions too.
When you look at the sharingan eyes, you can see black instead of white.