Some TMNT stuff really isn't for little kids.
Scarecrow plays on the fears of the unknown to inflict terror on his victims. An anarchist obsessed with using chemistry and psychology to spread and study fear. He joins the Society in order to sow panic on a global scale. He is an antagonist and playable character in Injustice 2.
Scarecrow is seen in the first scene in the swamp as a member of Grodd's society, transporting his Fear Gas to an unknown location. Deadshot becomes impatient over the process, though Scarecrow assures him that the gas will be delivered by tomorrow. When Poison Ivy captures a spying Green Arrow, Black Canary, and Harley Quinn. He sends Deadshot away and goes over to investigate. When Poison Ivy finishes explaining her motives in joining the Society, the trio of heroes escape via knife Harley had and Harley battles Ivy while Black Canary and Green Arrow take on Scarecrow. While Harley emerges victorious, Scarecrow had managed to subdue Green Arrow and Black Canary with his fear gas. He attempts to dose Harley with some of the gas, before Harley mocks the attempt, claiming she used to sniff the gas for fun. This hardly fazes Scarecrow, claiming that he had a new and upgraded batch of Fear Toxin and upon giving Harley a second dose, Harley envisions Scarecrow in his monstrous form. Scarecrow compliments her high tolerance, before engaging in a fight with her, with Harley emerging victorious. Upon his defeat, he gases Harley again, so she sees the Joker, but he is defeated by her, breaking the illusion. He is then seen escaping the swamp on a boat from Swamp Thing.
He is later seen gassing Wonder Woman, so she envisions Superman attacking her, stating she corrupted him and manipulated his grief. Wonder Woman manages to break the illusion by stabbing the illusion of Superman, before Scarecrow shows himself and gives her another dose to once again appear in his monstrous form. He is defeated by her and he tries in a last ditch effort to give her another dose, before Wonder Woman slashes his wrist, finally bringing him into submission. Wonder Woman presumably leaves him behind to save Supergirl from Cheetah.
He, along with the other members of the Society, disband once he learns that Brainiac will destroy the Earth, rather than let them conquer it.