Spoilers ahead for Legion "Chapter 15." Although Ptonomy's powers are prodigious, he has remained one of the least defined main characters on Legion… which makes the end of "Chapter 15" one of the most interesting developments for the mutant yet. What happened to Ptonomy on Legion, and what will his role be on the show moving forward? The memory artist fell victim to the delusion the Shadow King had planted in his head earlier this season, and he consequently ends the May 15 episode as a ghost in the machine — literally.
Given that the slimy delusion creature that crawled into Ptonomy's ear early in Season 2 was quickly followed by an outbreak of the contagion known as the Catalyst within Division III, you might have assumed that the two events were related — and that when the Monk died and the Catalyst was broken, Ptonomy was cured. But while the Catalyst was caused by the Monk, the delusion was planted by Amahl Farouk… and it's still been festering inside of Ptonomy this whole time, finally blossoming large enough to wreak havoc within Division III during the course of "Chapter 15."
The delusion causes Ptonomy to have visions of what's under Admiral Fukuyama's basket: a terrifying and monstrous insectoid-bird head. Believing that Fukuyama is a villain that needs to be stopped, Ptonomy sets out to kill the Division III leader… and infecting his fellow team members along the way in order to recruit them in his misguided mission.
While David is busy reeling from the news that Farouk had murdered his sister Amy in order to give Lenny a new body, Ptonomy is placing eggs around Division III that, when hatched, gave birth to delusions that crawled into the ears of Syd, Kerry, and Clarke, and ropes them into his paranoid pursuit of Fukuyama. Fortunately, David is able to stop them before they can murder the Admiral, who is finally revealed to have a very human — and very scared — face under that wicker basket he uses as a mask.
David is able to pull the baby delusions from the minds of his recently-infected teammates… but the original delusion inside of Ptonomy has apparently festered and grown to the point that it isn't so easily dispatched. It painfully emerges from Ptonomy's body, oozing out of his mouth and cracking open his spine, leaving the mutant a grievously wounded wreck on the floor.
While David confronts the oily critter, the Vermillion take Ptonomy's fate into their own hands. They drag him through the forest mural that serves as the backdrop of Fukuyama's room — and somehow into an actual forest — and plug Ptonomy into a tree. The last shot of the episode is of Ptonomy waking up inside some sort of computer; in order to save his life, Fukuyama apparently had to absorb him into his artificial consciousness. Ptonomy's body may be dead, but his mind lives on.
So what does this mean for Ptonomy moving forward? Earlier, I referred to the mutant's new status as the "ghost in the machine." That phrase actually originates from Descartes' theory of mind-body dualism, which posits that there are two distinct aspects that make up personhood: the body (the machine) and the soul/mind, as separate from the brain (the ghost). If you are brain-dead, are you really a "person"? Descartes wouldn't think so; there's more to being a person than mere corporeal form, in his opinion.
In that aspect, Ptonomy lives on, even if his physical body is dead. And the idea that a subjective mind is just as important — if not more important — to personhood as an objective physical body is very much in keeping with the themes of Legion and its explorations of reality and insanity.
Perhaps Ptonomy will be even more powerful now that he's unshackled from physical form. Or perhaps this development will be a disaster; if he's still infected with some small part of the Shadow King's delusion, he could end up bringing down Admiral Fukuyama and Division III from the inside.