Smylex was the Joker's codename for his poison that left frozen grins on its victims. It appeared as green or sometimes purple vapor, usually causing people to spasm and laugh uncontrollably.
Joker later laced random ingredients to hygiene products with components of Smylex. When certain hygiene products were applied in specific combination, they would fall victim to the poison.
DDID Nerve Gas
Jack Napier kept a stolen CIA file on his desk at Axis Chemicals. How Napier obtained the folder is unknown, but it contained information and photos of an experimental nerve gas known as DDID. It was discontinued in 1977 as it caused victims to violently convulse, with their facial muscles pulled taut in a rictus grin. It was likely deemed a violation of the Geneva and BWC protocols. Joker spread hundreds of photos of poisoned soldiers on the floor of his studio room.
Using his aptitude for chemistry, Joker began to concoct his own custom version of the poison that would cause uncontrollable laughter before death. He began to work with a scientist employed at the facility on how to distribute it in the raw chemical component products shipped from Axis.
Joker taped a taunting "commercial" that would interrupt an Action News report breaking the first news of its victims, models Candy Walker and Amanda Keeler. Photos of the models with super-imposed lips saying "Love that Joker!" accompanied him in the commercial. A live, unpoisoned, gagged and bound hostage was seen in the tape next to an unidentified male corpse suffering the effects of Smylex. Elaborate sets and faux Smylex product props were made by the Joker's men for the threatening video.
The Joker began to spread terror in the city, first by lacing hygiene products with a deadly chemical known as "Smylex", which caused victims to laugh to death when it was used in certain combinations. The Joker then set a trap at the Flugelheim Museum for photojournalist Vicki Vale, and he and his Goons vandalized the surrounding works of art over the corpses of poisoned civilians. Batman arrived soon after, rescued Vicki, and the pair escaped in the Batmobile. Batman gave information about Smilex to Vicki so that she could warn the city via the press about the poisoned products. Alexander Knox was the first to break the story in print, with a front page story on the Gotham Globe.
Batman later used his communicator to send the Batmobile into the Axis processing plant to drop an explosive. This resulted in a large series of chain reacted explosions, destroying the source of the poison. Joker taunted Batman from his green helicopter to let him know he had accomplished little and the parade was still on.
Meanwhile, the Joker's army of goons had amassed at the 200th Anniversary Parade with a promise to give away $20 million in cash. When the citizens arrived, however, Joker attacked them with Smilex that spewing from the inside of his giant balloons. Batman arrived on the scene and saved Gotham from the attack by using the Batwing, pulling the balloons away from the crowd.
This chemical weapon was never seen again in the city.
Arkham Game Series
As seen on gas-canisters in the games, Joker's laughing gas is canonically referred to as Smilex.
While not appearing directly in the film, Harley Quinn is wearing a t-shirt which says, "Smylex" on it.
Behind the Scenes
- This chemical weapon was based on the comics' "Joker Venom", and any other alias for the poison that left the Joker's victims with a postmortem rictus grin.
- In Sam Hamm's original script, the first time that we saw Smylex's effect (called Smylenol in the script) was on the two female models, who were only represented as cardboard cut-outs in Joker's commercial. The original scene had them in a bikini photo session with a photographer. The photographer urged them to smile more as he snapped away. The girls began to giggle, which at first pleased the photographer. Soon, their giggles became laughter before they became uncontrollable helpless hysterics, which had the photographer going from mild annoyance to complete horror as the exhausted girls expired from forced hilarity, with the ghastly Joker-like grins that were frozen on their faces.
- As it was originally intended, the death scene was much more protracted than the one with the female newscaster, which depicted death by Smylex as a particularly agonizing, if mirthful, way to go.
- In the novelization of the film, the photographer was revealed to be Vicki Vale.
- In the film Charlie and the Chocolate Factory (2005) directed by Tim Burton (the same director behind Batman and Batman Returns), Smilex is the name given to a brand of tooth-paste as an easter-egg to Burton's history with Batman.