Floro has developped a hatred of most people as he has witnessed their greed in consuming all of the planets resources and the pollution that they bring about. Causing destruction to all of the natural plant life around them. So he seeks revenge on people in order to aid his fellow plants. He might make exceptions for people that he sees are kind to nature.
Floro's legs are made of roots, which are flexible. He usually just twirls them together to form feet for easy maneuvering. But he can untie them to use them in all sorts of ways. They're also how he consumes nutrients. To do so, he needs to dig himself into the ground (like a normal plant) and his roots can absorb the nutrients found in that soil. A rich source of nutrients being decaying things. So killing people and burying them is how he's able to consume a lot of nutrients.
Floro also has tiny versions of himself sprouting all over him at any time. Once big enough, they can actually pop off of his body and attack (they bite).
Floro doesn't speak, mostly just grunts.
He possesses extraordinary strength (think the Hulk) and has a tremendous will to survive. He doesn't necessarily have organs, so there's no specific weak spot that would fatally wound him.