This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Punisher
Punisher POV. Its main villain is a case of Body Horror thanks to toxic waste, and when he bites a pregnant woman, she gives birth to mutated a baby that slaughters it way out of a hospital and has to be confronted in the sewers below.
Frank Castle's own death during the Dark Reign also counts. There are few sequences in the Marvel universe that so effectively and blatantly present the risks of Bullying The Dragon, as Punisher's stubbornness and arsenal are pitted against the regenerating Daken, who proves just how useless they are. Daken starts by shooting him and blowing him up with grenades, seemingly just for kicks. Then the mutant closes to hand to hand range, where he pummels Punisher mercilessly, breaks his leg, slices his throat open, hacks off a limb, and, finally bored of it all, cuts him into pieces with the ease of an industrial meat slicer.
The Hood attempts to get the Punisher to leave his organization alone bu offering him the single thing he could possibly ever want - the return of his wife and children. Hood brings them back with the same magic he used to temporarily resurrect a group of supervillains (not zombies, their actual living selves), and offers to make the ressurection permanent if Punisher agrees. Punisher promptly burns them alive with his flamethrower angrily declaring that his family is dead. Even Hood is horrified. the reader is never shown whether or not what Hood brought back was Frank's family, they're never shown on panel or speaking, and a later issue reveals that no, they were not real
Frank is understandably plagued with doubt and guilt over his action, uncertain if what he destroyed was really his family or not, and during his time as Franken-Castle, has a nightmare about embracing his burning wife and children, declaring and both they and him "belong dead".
Punisher himself is this in-universe, especially in his early days when superheroes simply did not kill. It just wasnt done. He's especially this to the Maggia and other crime syndicates. While they occasionally run into superheroes (especially Daredevil), they're usually below the concern of the metahuman community who is too busy trying to keep various cosmic threats and mad scientists from destroying the planet. The Punisher on the other hand has made it his life mission to annihilate them. And unlike their crews of poorly trained greaseballs and thugs, the Punisher is a SOLDIER, an elite fighting machine who is almost impossible to stop.
Pictured above, archenemy Jigsaw, a cruel gangster whose face was disfigured by the Punisher smashing him through a window. He abused his son and helped the Hood beat up Tigra.