All For One is a pretty terrifying villain even by My Hero Academia standards. Besides his raw power, his ability to steal people's Quirks, and his menacing appearance, he has the determination to see his dark ambitions through no matter what. That kind of desire can lead to some pretty heinous acts. Nowhere is this more apparent than in the latest chapter of the manga.
Chapter 356, "Regarding the Enemy," showed readers All For One's horrifying response to his Quirks rebelling in the previous chapter. In the vestige world, he began to hunt down and destroy the rebellious Quirks in order to regain control of his body. In a lot of ways, this act and the gruesome way it was depicted were reminiscent of Francisco Goya's 19th-century painting, Saturn Devouring His Son.
For context, here's how the situation originated. In Chapter 355, "Extras," All For One found himself being held back internally by his own stole Quirks. Normally, the wills of other Quirks, or "vestiges," remain dormant when they're stolen by All For One. However, for one reason or another, they started moving against him; this was represented by scenes of All For One in the vestige world being grabbed and pulled down by those whose Quirks he'd stolen. The resulting delay left him vulnerable in the real world long enough for the Heroes to land decisive blows and destroy his life support mask.
Despite the valiant efforts of the stolen Quirks, All For One was determined to win this fight, so he did the only thing he could. His vestige self began cannibalizing the rebellious Quirks; this likely meant destroying his own Quirks, but it was the only way to regain control. The image of a giant All For One grabbing and consuming the vestiges was haunting, to say the least.
All For One eating his Quirks is eerily similar to the painting Saturn Devouring His Son in terms of story and imagery. Like All For One, Saturn feared that his children would fulfill a prophecy that involved overthrowing him. His solution to this was to consume them before they could fulfill their destiny. Both of these powerful rulers sought to overcome their potential insurgencies through violent and savage means.
What makes Goya's representation of Saturn particularly unsettling is his sense of macabre. The act of cannibalizing one's own children is already inhuman in its own right, but Goya's presentation really drives the point home; Saturn is kneeling in the dark naked and hunched over; he has a frantic look in his eyes and his mouth is a gaping, black hole; his hair is long and unkempt; his son's right arm and head have already been reduced to stumps and he's working on the left arm. Words can't describe the cruel savagery in this painting.
All For One devouring his Quirks, while not necessarily as gruesome as Saturn Devouring His Son, is equally creepy. This can be partially attributed to how alike the two scenes are in their presentations; All For One holds onto his victims just like Saturn does; both of them go about eating their prey in similarly animalistic manners; All For One doesn't have Saturn's hair or eyes, but he definitely has the gaping maw, not to mention the long row of teeth; the backgrounds of both works are similarly dark, though All For One's other victims can be seen burning alive in his background; All For One's current meal may not be missing their arm or head, but the look of terror on their face more than makes up for it. If Horikoshi ever came out and said he drew inspiration from Goya's painting, it wouldn't come as a surprise.
Of course, knowing that this type of cannibalism has been shown in art before doesn't make it any less difficult to look at. Seeing someone else get eaten alive is a scary thing to behold, whether it's by All For One or Saturn or anybody else. What makes their situations especially troubling is that they were brought about by a desperate desire to maintain control; one can't help but wonder what they would do to ensure their place in the world wasn't threatened. As long as All for One shows this much monstrosity in all his endeavors, he'll be sure to strike fear in his enemies.