Immunity to all poisons, viruses, bacteria, fungi, and Joker venom. Okay so in Arkham Knight, Ivy sacrifices herself in order to save Gotham when Scarecrow unleashes a massive amount of fear toxin on the city. So she can be poisoned and die, but the scale is really massive, as she basically absorbed the toxin covering the entire city of Gotham.
Pheromones that make people susceptible to mind control, although strong-minded people like Batman are usually capable of resisting. She was even once able to control Superman with the help of kryptonite.
She can control plants with her mind.
Semi-mystical connection to the plant world through a force called the Green. Basically she can talk/listen to people through plants.