Q's cruelest trick involved tricking Captain Jean-Luc Picard into resurrecting his younger brother Claude from the dead so he could grow up to become a dictator in a Star Trek: The Next Generation comic. And that wasn't even the worst part of Star Trek: The Gift, from John de Lancie, Gordon Purcell, Pablo Marcos, Julianna Ferriter, and J.K. Woodward.
In the non-canon issue from DC Comics, the powerful entity known as Q messes with Picard by transforming him into different forms and then hurling him back through time. Terrified by Q's goading, Picard goes to check on his parents, only to discover the alien entity masquerading as his young self. Q's real plan is for Picard to have to prove his identity to his parents by sharing intimate details about his life so that Q can do the same and counter with a rather painful memory.
When it's his turn, Q recounts the tragic occasion when Picard refused to play with his younger brother Claude, and when they went looking for him later that night, Claude had fallen down a well and snapped his neck. Sharing this horrific memory, however, backfires spectacularly because Picard's parents tell Q that their real son would have never made them relive such a horrible ordeal. In the moment, it appears as though Q shared such a personal moment to win and ended up losing because he doesn't understand humans, but really it just sets up the next stage of his plan. As a gesture of kindness, Q offers to resurrect Claude, and despite expecting a trick, Picard can't help but agree for the sake of his parents. However, it turns out that Claude's accidental death was a gift in disguise, as he was destined to become a despicable tyrant who would contort the Federation into a dictatorship and wreak havoc on the galaxy.
But the endpoint of this whole experience wasn't just Q proving to Picard just how deplorable humans are, or teaching some twisted life lesson. Things get so bad that Picard is actually manipulated into giving Q permission to murder his brother for him. Although Q later wipes Picard's memory of the entire experience, it's still horrific to think that he not only forces Picard to relive a devastating memory that he undoubtedly feels responsible for, but makes him an accessory to the murder of his brother.
While this is one of the most twisted psychological tricks perpetrated by anyone in the Star Trek universe, even by Q's standards, the story adds some additional context to an actual event that transpires in Star Trek: The Next Generation, revealing just how much a rather unpleasant predicament impacted Q. Star Trek: The Gift takes place just shortly after the monumental "Deja Q" episode where Q seeks asylum on the Enterprise after the Q Continuum strips him of his powers. While it's understood that the incident was traumatizing for Q, The Gift proves that Q having to rely on a species that he enjoys ridiculing affected him on such a profound level that he felt compelled to manipulate Picard in the most twisted, humiliating way possible.
Q has proven his disdain for the human race and has enjoyed terrorizing Captain Jean-Luc Picard in particular, but this was a much more personal attack than anything he ever perpetrated on the Star Trek TV show, and the issue offers an even better glimpse at Q's true power, as he manipulates time, space, and reality to continuously manipulate the one person who truly knows he can't be trusted.