Joker Venom

Joker Venom is a chemical formula created by the, which appears to be the substance that disfigured him and drove him insane. While the Joker was incarcerated in, approached him with the offer of  in exchange for the formula for Joker Venom. After and Ra's al Ghul found the Joker in his cell, Joker coughed up a piece of paper with the formula on it.

After he mutated himself and the other Arkham inmates, the Joker also discovered that mixing Joker Venom with mutagen would not only transform the victim, but also make them violently insane. He used this mixture to mutate, but the effect of the Joker Venom was negated when the mutation was reversed.

Large quantities of Joker Venom were produced at Ace Chemicals by Shredder and Ra's al Ghul, and some of the substance was loaded onto a to be mixed with mutagen and rained down on the citizens of Gotham City. However, the mixture was ultimately destroyed, as was the supply of Joker Venom.

The Shredder was thrown into a large vat of Joker Venom, which had a similar effect to that which had disfigured the Joker.