"I guess it's like what they say. We all could go insane with just one bad day. I guess with you it's more like one bad spray! You'll see..."
Jerome Valeska to Jeremiah Valeska[src]

The Laughing Toxin is a powerful nerve toxin created by Scarecrow that attacks the nervous system of its victims, causing a slow, painful death. When inhaled, it induces fits of laughter, then stretches its victims face into a pale grin shortly before death.


The Laughing Gas is an altered version of Scarecrow's Fear toxin, however instead of making people see their worst fear, it alters their face to a clown-like visage and causes them to die laughing. On Jerome Valeska's orders the members of the Legion of Horribles were going to spread the toxin onto Gotham and drive everyone mad. As soon as Penguin found out, he knew there might be nothing left of Gotham to rule over and contacted Jim Gordon to help stop the catastrophe. Jerome had Scarecrow and Jervis Tetch drop the Toxin by Blimp starting with town square. Luckily, Penguin managed to stop the Blimp driver and saving Gotham from the Toxin. Unfortunately, Jerome managed to expose his brother Jeremiah Valeska to a version of the toxin that wouldn't kill him upon mutation so he could continue Jerome's work.[1]


Jeremiah Valeska driven mad by a specially altered version of the toxin.

Once the victim has inhaled the toxin, they will start to laugh uncontrollably. As the laughing continues the victim's face will be forced into a grin with their skin turning white. As they reach the final stage, the victim will cry blood from their eyes and eventually perish from asphyxiation.[2]

The one known exception was Jeremiah Valeska, who was given a modified version of the toxin. Initially the effects were the same, but Jeremiah neither wept blood nor died from his exposure, and he apparently stopped the hysterical laughter after a short time. Except for the change to his physical appearance and a newfound extreme sense of ruthlessness, he remained much the same as he had been before his encounter with the toxin. It is unknown exactly how much Jeremiah's mental health was affected by the gas, as he displayed repressed signs of mental instability beforehand, but the gas certainly brought those instabilities to the surface and amplified them. It did not affect his demeanor or his intellect significantly, however.[3][4]


Season 4

People exposed to the Laughing Toxin


  • The Laughing Toxin is a reference to the Joker Venom, The Joker's most famous and iconic murderous weapon in the DC Comics.


  1. Cannon, Danny (writer) & Copus, Nick (director) (April 12, 2018) "A Dark Knight: That's Entertainment" Gotham. Season 4. Episode 18.
  2. Lilien, Steven & Wynbrandt, Bryan (writer) & Vrvilo, Maja (director) (April 5, 2018) "A Dark Knight: Mandatory Brunch Meeting" Gotham. Season 4. Episode 17.
  3. Cannon, Danny (writer) & Copus, Nick (director) (April 12, 2018) "A Dark Knight: That's Entertainment" Gotham. Season 4. Episode 18.
  4. Huston, Charlie (writer) & Milto, Louis Shaw (director) (May 3, 2018) "A Dark Knight: That Old Corpse" Gotham. Season 4. Episode 20.
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