I played around with something along those lines, but it was called a Vivimancer. In some respects the class was as repulsive as the Necromancer because they liked to experiment with life forms, making modifications, adding parts, and so forth. You could, for example, conceive of chimerical life forms as the products of Vivimancer experiments. They might live inside giant hollow plants or trees that they have modified to serve the purpose. They would be masters of diseases, toxins, organ transplants, &c. They may live for long periods because they have mastered rejuvenation through body part transfers, but they could be hideous in appearance due to parts from various creatures. &c. 
Do you have something in mind for a class?

Do you have something in mind for a class?