The Justice League of Arkham was formed by Batman and he led the team consisting of Nightwing, the Joker, Catwoman, the Riddler, The Ventriloquist and Scarface, and Poison Ivy.
Justice League of Arkham
After learning of the mysterious Advance Man's plan to release a toxic gas that reacts with water in Gotham City, and learning that when the toxic gas mixes with the water it kills every form of life that it encounters,Batman freed The Joker from the Slab' and he also freed The Riddler, Poison Ivy, and The Ventriloquist from Arkham Asylum so they could aid him in stopping the Advance Man. Along with Catwoman, the newly-formed Justice League of Arkham broke into the processing plant that the Advance Man was planning to release the toxic gas in and captured him. While interrogating him, the Joker escaped and both Batman and Nightwing went to find him. During this time, the Advance Man convinced the remaining super-villains to abandon Batman. After they left, the Advance Man was able to free himself and he teleported away to San Francisco.
Trivia
Justice Leagues was a six-issue crossover event published by DC Comics in 2001. In the mini-series, alien invaders used Hector Hammond, a telepathic supervillain, to make the world forget that the Justice League of America had ever existed, only to find the individual members of the Justice League instinctively creating new crime-fighting organizations beginning with the "Justice League of A" to fill the void. Each issue was supposedly the first of a new series featuring one of the alternate teams, although they were really one-offs except the last, which featured the recreated Justice League of America.
Featured JLAs were the "Justice League of Aliens", led by Superman and the Martian Manhunter; the "Justice League of Amazons", led by Wonder Woman; the "Justice League of Arkham", led by Batman; and the "Justice League of Atlantis", led by Aquaman. Cameo appearances were made by the "Justice League of Adventure", led by the Flash (Wally West); the "Justice League of Air", led by Green Lantern (Kyle Rayner); the "Justice League of Anarchy", led by Plastic Man and Harley Quinn; and the "Justice League of Apostles", led by the angel Zauriel.