The green goo was a substance discovered in the sewers of Bludhaven. It appeared to cause an emotional response in anyone who came into contact with it, resulting in instant rage. Early experiments also demonstrated it could take control of brain matter to become sentient in its own right.
The green goo was eventually tracked by the gang to a secure store in the sewers of Bludhaven, operated by LawTech. Leaking barrels within the store were the cause of the contamination in the sewers. The green goo stored within was ultimately destroyed by Guldar, who disposed of it by throwing it into the sun. The origin of the goo and whether any more exists remains unknown.