Some nice feats for Grundy vs Amazo. He controls his completely severed arm, reattaches it, and heals from Amazo initial laser attacks. He goes on to decapitate Amazo, and Amazo flees after the swamp starts attacking him.
Grundy was being possessed by something that wanted him to become a plant elemental. Grundy blamed Swamp Thing and literally grinded him to a pulp. Grundy then bathes in a vat of acid chemicals to remove his greenish appearance.
How is it not PIS? Grundy could have finish drowning him, then remove his cowl. Grundy was being control by Grodd as were a lot of villains who was trying to take down Bats and Supes. And Batman is a walking plot device anyway, Grundy has resisted all types of gases from Green Arrow's specially made gas arrows to Poison Ivy's toxins. But only Batman's seems to work.