Warning: contains spoilers for Star Wars Adventures: Shadow of Vader’s Castle #1!
The Joker has employed a staggering number of disturbing methods to torture and murder his victims throughout his decades-long career of villainy. But the tactic he most has an affinity for is Joker Toxin, a venom that makes his victims laugh uncontrollably - usually to death. While many pop-culture villains have incorporated the use of toxins into their master plans to some degree, one antagonist in particular who most would never expect to resort to such a strategy is Darth Vader, and yet the Sith Lord has his own version of the aerosol weapon.
The Joker has created both fatal and non-fatal versions of the Joker Toxin, the latter of which causes victims to laugh so hard that their faces contort into an unnaturally large grin, while their eyes bulge out of their sockets. Utilizing many of the chemicals that first created the Joker, Joker Toxin sometimes causes skin to whiten, hair to turn green, and mouths to stretch back in a rictus grin. Those who have been exposed to these toxins for a prolonged period of time suffer permanent brain damage, though hallucinations and huge shifts in personality can happen in seconds.
What Darth Vader ends up doing is comparable to using massive doses of the non-lethal Joker Toxin in the first issue of Star Wars Adventures: Shadow of Vader’s Castle by Cavan Scott and Francesco Francavilla. Of course, Vader is too deadly to need to pre-mix his toxin; he just needed the toxic fumes emanating from Mustafar's lava lakes to do so.
The fumes of the lakes cause hallucinations, referred to as “shadows of the mind,” and prolonged fits of laughter. His victim in this case is an Imperial inspector who originally comes to Mustafar to ascertain why stormtroopers’ minds have been snapping while on assignment at Vader’s castle on the Outer Rim’s fiery planet. The officer is understandably skeptical at first, but upon experiencing the fumes firsthand, he quickly recommends that Vader allow his troops to evacuate temporarily before attempting to leave himself as he begins to experience some unpleasant side affects from ingesting the fumes. But Vader doesn’t let him leave. He wants a servant who can attend to his needs while on Mustafar, and he believes this inspector is the best candidate he's had so far. So he uses the Force to keep the inspector in place and essentially commands him to embrace the shadows that have begun invading his mind.
Darth Vader oversees this poor soul succumbing to madness for days, during which time the inspector continually laughs uncontrollably throughout the entire ordeal. Like Joker’s victims who sustain permanent brain damage after ingesting his venom for extended periods of time, the inspector suffers a mental break that creates an alternate personality: Vaneé. Joker has used his chemical for similar goals in the past, helping to create longtime henchwoman Harley Quinn. It's unusual for one of pop culture's most stoic villains to steal a play from one of its most manic, and yet when it comes to evil, neither character is known for balking at what it takes to get what they want.