Pamela Isley is an unusual foe for Batman. Ivy is in fact a plant Human Hyrbid which was the result of Professor Jason Woodrue experimenting on her.

Ivy developed a closeness to plant life and considered herself to be their protector. She has often come up with schemes to benefit her financially or to seek revenge on those who kill plant life. She also uses her ability to release pheromones to seduce and control men.

Other Info
-Even touching Poison Ivy's body can be deemed fatal at times.
-Poison Ivy's bizarre body chemistry has one added benefit: She is immune to human diseases and plagues
-Jason Woodrue is also a supervillain called the Floronic Man.