Joker venom
Joker venom is a fictional toxin, a favourite murder weapon utilised by The Joker in the Batman franchise of movies, comics, and cartoons.

# Analysis
Joker venom can exist in liquid and gas states and has been used to great effect. The gas form is slightly denser than air and in some portrayals dissipates over time.
The DC Technical Manual: S.T.A.R. Labs 1993 Annual Report (a sourcebook for Mayfair's DC Heroes Roleplaying Game) stated that Joker Venom is "a hellish mixture of hydrogen cyanide and Strychnodide (a strychnine derivative), the toxin causes immediate cessation of heart and brain functions.  As a side effect, the victim's muscles contract in such a way as to severely tighten and discolor the victim's skin, especially in the facial area.  This leaves the victim's corpse permanently scarred with a clown-like grin in tribute to his killer.  Since the Joker Venom is just as deadly if absorbed through the pores as it is if inhaled, the Joker occasionally releases it in gas form throughout the central heating/cooling vents of a building."
How exactly Joker knows how to make the venom varies by story. In the graphic novel Batman: The Killing Joke, it was revealed that the man who would become the Joker once worked in a chemical plant, and may have had some chemical education as a result.
In the 1989 movie, when Bruce Wayne reads through the police file on Jack Napier, he learns that Napier, despite his criminal ways, is extremely intelligent and especially gifted in chemistry. Napier, who became the Joker, was inspired to make the poison after reading testing reports on a nerve-affecting chemical that was (presumably) a component in the vat mixture caused his metamorphosis.
The 2004 graphic novel Batman: The Man Who Laughs revealed that Joker, who was created via way of the chemicals, had stolen them in a plan to poison Gotham City's resevoir, but the plan was foiled by Batman. A story arc in Legends of the Dark Knight revealed that a cousin of the man who became the Joker, Melvin Reipan, a master chemist but an idiotic buffoon otherwise due to an idiot-savant condition, was persuaded to create the Joker Venom as a way to "make people laugh", in exchange for becoming "handsome". However, Reipan was in fact physically very attractive, only having been told by his abusive mother he was ugly. This story appeared in Batman: Legends of the Dark Knight #50 and not only revealed the origins of Joker Venom, but also told the first battle between Batman and the Joker after his first attempt to destroy the city.
In a 1980s comic book, the Joker facilitates one of his many escapes from Arkham Asylum using the venom - by mixing together the common cleaning chemicals found in a janitor's closet.
Marvel Comics has an apparent equivalent to Joker venom in the form of Red Skull's "dust of death", a chemical which turns the head of its victim into a "red skull" resembling that of Red Skull. In a crossover, the Red Skull and the Joker face off against one another, the Joker angry he had unwittingly worked for a Nazi(I'm a lunatic, but I'm an American lunatic!), and employ their favourite toxins on each other-realizing they are useless, as they are immune to their own, and both toxins are strikingly similar at chemical level.

# Effects
- Lethal version
Contact with Joker venom causes uncontrollable spasms of laughter and then causes a painful death. Some have speculated that the venom hyperstimulates the laughter functions of the brain and the victim is unable to breathe.
- Non-lethal version
Prolonged exposure to the non-fatal forms can cause permanent brain damage.
The venom causes uncontrollable laughter, but instead of dying, their faces are usually pulled into an unusually large grin. Artists often stylize the effects, adding yellowed teeth, bulging eyes, etc. similar to the features of the Joker himself.

# Usage
- Comics
Joker venom has been a part of the Joker's arsenal since his first appearance in Batman #1 (1940).  The venom is often deployed as an airborne agent, but can also be used in its liquid form (used both to poison victims through their unwitting consumption of it, or in special darts). In Batman: The Killing Joke, Joker was seen to use a spike worn in his palm (similar to a Joy Buzzer) to administer the drug in a handshake manner.  In Jeph Lobe's and Tim Sale's Catwoman: When in Rome Joker venom is duplicted by the Riddler to blame Catwoman for the murder a mafia king pin in Sicily.  It is referred to as Joker Juice by both Catwoman and The Riddler.
- Batman: The Animated Series
In the 1990s animated series, Joker venom was almost exclusively a non-lethal gas, or, as seen more often, infected individuals are almost always revived before death (the venom doesn't kill as quickly in the series). It was also used as part of a binary compound in an episode called "The Laughing Fish", in which selected targets were exposed to part of the compound and later gassed with the second part, thus the venom would only affect the intended party. That same episode also featured a diluted version of the toxin, which only affected fish to make them smile (though as Joker later revealed in "Mad Love", the toxin was ineffective on piranha), as part of Joker's plan to sell "Joker Fish" and earn money off product sales (Joker also indicated a possible plan to alter the toxin to affect cattle should the fish plan not work- a hint that Joker could alter the toxin to affect any specific species of life he wished). In later movies and episodes, the venom became lethal (it was used to kill, among others, Sal Valestra in Mask of the Phantasm, a security guard in "Holiday Knights" and a government agent in the Justice League episode "Wild Cards"), although Joker also used the non-lethal variant as well. Joker did not appear to be immune to it, as evidenced by his protective helmet in "The Last Laugh" (although this may have been an oversight - later episodes showed him breathing and even talking while the gas is in the air around him). However, in the episode Harley & Ivy, Poison Ivy did display immunity towards it due to her immune system's resistance to toxins.
- Batman (1989 film)
Dubbed Smilex (sometimes spelled Smylex) by the Joker, the venom originated as did nerve gas, an experimental bioweapon developed by the U.S. Army and discontinued in 1977, according to a file seen in the Joker's lair (the date may have been chosen to coincide with President Jimmy Carter's order for the cessation of U.S. biological weapon production that year).  Smilex was distributed both as a gas and in liquid form, mixed as separate components in various beauty and hygiene products which only took effect when the victim used a number of them in tandem, thus making the toxin impossible to trace. The Joker shows no immunity to it, and can be seen donning a gas mask during the mass gassing during Gotham City's 200th anniversary parade scene.
- The Batman (new TV series)
Both versions of the venom are used in the new cartoon. The non-lethal version is weaponized as a gas and seems to dissipate over time. The gas is called "laughing gas", and puts its victims into a coma. Batman provided an antidote to this laughing gas. However, Joker also has a lethal version which is a liquid. The effects of this venom are the same as the one used in the Joker's first appearance in the comics (a venom which takes 24 hours to kill.). In the meantime, the victim slowly has fits of laughter until they are unable to function and die with Joker's trademark grin. Batman was infected with the venom, and was able to make a cure for it as well before it was too late.

# Cures
It has been stated that the Joker constantly alters the formula to the Venom (which he is immune to) so no antidote can be prepared for it. However, there have been some antidotes concocted. Gotham Police Commissioner Jim Gordon had been poisoned with the venom; and was successfully saved. It took days for the effects of the venom to get completely out of his systems.  During that time, he found black humor funny; although normally, that would be out of character for him.
Poison Ivy concocted a fast-acting antidote for Joker venom. In Harley Quinn #13, Harley asks Ivy why she did not save people under the venom's influence, to which Ivy replies, "I don't do that, Harley. I don't save people. I'm poison, remember?"

# Aliases
Joker Venom has had a variety of names depending on the writer. They include:
Smilex
Laughing Gas,
Joker Gas,
Joker Juice,
Laughing Toxin,
Laugh-A-loads
and Perma-Smile