Since I was the titan that kinda made Biomancers, I'll guess I'll explain how they work.
A Biomancer controls life. He can take it away, and he can give it. The question is the price. Where does the life go if taken, or where does the life come from when it's given? A Biomancer works on conservation of mass, or more simply having a bank account that liquidates itself after a certain value you don't really know. He can store life, but it's like water filling a cup. If he is almost empty, then he can almost fill himself to the brim with human life. If he is recently filled, he can barely hold half an insect's soul. If you hold too much, then the water leaks out onto the table. This is not good. Life begins to twist it's surroundings in bizarre ways. Inanimate objects gain personality, trees grow massive and more like fauna then flora, animals and humans become more fauna then flora, and the dead begin to rise. Now, when you give, it's a lot less complex. Give too much, you die. That's it. The life of a Biomancer is mainly being a serial killer and an angel, sometimes at the same time. To give, you must take, is a popular motto. The problem is that souls are hardy things and the soul when fused with another can lead to complications. A baby with the knowledge of a scholar, a man with the intelligence of an ape and/or a child with the memories of the guy whose soul you ripped out. It's a very very very tricky business, but it has a lot of perks and can get you some respect. Or hanged. Depends on how you justify yourself to a crowd.
Warning, will not stop Slask from ripping you apart for murdering anyone of his tribe, entering his forests, being a jerk who doesn't like Biomancy or just being related to Promidalchus.