Season 5, Episode 1 - "The Batman/Superman Story, Part One"
Batman and Superman find themselves teamed up when Lex Luthor begins his operations in Gotham City to take down his arch-nemesis, and employs a horde of the Batman's villains to do so. Lex later on gets ahold of Poison Ivy's control gas, and laces it with Kryptonite, and now becomes able to control Superman's mind.
