These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Swamp Thing
Author's Saving Throw: The first arc of the fourth series is dedicated to undoing everything that occurred in Brian K. Vaughan's run.
Complete Monster: Anton Arcane is a scientist turned Evil Sorcerer obsessed with immortality and its secrets. First seen attempting to steal the Swamp Thing's body, Arcane failed and died in the attempt. His soul, however, returned from hell to steal the body of his niece Abigail Arcane's husband, Matthew Cable. In the guise of Matthew, Anton raped Abigail and consigned her soul to hell in his place. In his new position on earth, Arcane attempted to drive reality itself to insanity, using the souls of resurrected serial killers to cause destruction as the innocent succumb to savage, homicidal urges.
In the New 52, Anton Arcane's new incarnation is a being of boundless cruelty. In his pursuit of immortality, Arcane took over the elemental force of The Rot, the natural force of death and decay and subsumed it to his will. Arcane extends the Rot to devour all that lives and trap the world in deathless limbo he can rule. Arcane even forced his own nephew to be the Rot's avatar, devouring his mind from within. In Arcane's battles with Swamp Thing, Alec Holland saw a future where Arcane gruesomely tortured and beheaded Abigail and saw lobotomized clones Arcane had made of her as cannon fodder.
Fanon Dis Continuity: People tend to view the series solely in terms of the Alan Moore run, which may partly be due to the fact that the rest of it has either never been collected in trade form or is otherwise notoriously difficult to find. It's generally accepted that the Wrightson-Wein run is pretty good, if much more straightforward and smaller in scope, while the Brian K. Vaughan run...isn't.
My Real Daddy: Len Wein helped create Swamp Thing (and more), but Moore's complete rewrite of the character is the one that lasted.
Nightmare Fuel: There's a lot of it, especially after Allan Moore took over and turned it into an active horror series for the Vertigo subverse.
One prime example is Nukeface, introduced during Saga of the Swamp Thing #35. Very little information is given about the guy, which ultimately makes him more disturbing, but he's basically a mad, disfigured old vagrant with a gaping mouth fall of half-rotted teeth and flesh rotting off of his face, courtesy of having become addicted to drinking nuclear waste. He's so full of radiation that his presence irradiates others, his touch can kill (especially when used against Swamp Thing), and he's so crazy he's oblivious to the fact he (frequently) ends up killing people in a horrific way by either touching them, his mere presence, or offering them a swig of his own toxic "moonshine". And then there's the scene where Wallace Monroe, accidental "creator" of the nuclear vagrant, discovers his heavily pregnant, gentle and very religious wife actually found Nukeface out in the swamp and tried to keep him warm with her shared body warmth, resulting in him and the police with him backing away from the now heavily-irradiated woman, who has no idea why they're running from her and begging them to tell her what's going on...
Abby learns the reason her husband Matt Cable has become much more assertive, capable, and passionate: he's been possessed by her uncle, Anton Arcane. The fact that she'd unknowingly had sex with her evil uncle isn't the worst part. Matt was possessed willingly as he lay dying after a car accident.
Abby's reaction also belongs here: after increasingly hysterical attempts to wash herself clean of Matt/Anton's touch, she tries to scrape it off with a wire brush.
There's also the bit at the end of Moore's run on the series where a Corrupt Corporate Executive responsible for disrupting Swamp Thing's connection to the Green, effectively killing him for a while, makes the mistake of eating a sandwich with lettuce as Swamp Thing's consciousness returns to Earth.
The stories set in Hell is more than a little frightening. We have Anton Arcane's torment mentioned down below but beyond that, we see corpses impaled on giant hypothermic needles, nasty demons that go far beyond the more traditional descriptions, mutilations, rape, and more.
The young victims of the Monkey King had some pretty horrific fears, even before the little shit started to make them manifest in those poor kids' bedrooms.
Squick: Anton Arcane, especially after he possesed Matt Cable's body.
Tear Jerker: "Pog". Notable in that the characters aren't even regular cast members, and in 23 pages...well, damn.
To go into further details, the short story "Pog" revolves around a bunch of strange-talking Funny Animal aliens (essentially a sci-fi Lawyer-Friendly Cameo of the characters from Pogo) landing in the Louisiana swamp. The Captain Ersatz version of Pogo explains to Swamp Thing that he and his friends are the only survivors from his world, forced to flee after the monkeys went insane and took over, first socially restricting the other races, then using them as medical experiment test subjects and food, and they hope to find a new world to settle on. Swamp Thing, unable to communicate verbally with the alien, instead leads him mutely to the nearby human town of Houma, where the captain breaks down weeping that the same thing that drove him and his people from his world is happening here.
And then there's what happens when the Albert Alligator expy finds some Louisiana alligators and rushes to them, calling them kinsmen. Being Earth gators they are, naturally, not sapient, and so he is promptly killed by them, forcing his friends to bury him on an alien world and fly away to continue their lonely search.
Abby has a daydream at Swamp Thing's funeral. In it, Swamp Thing comes back to life, and he and Abby agree to marry. Everyone who discriminated against their love apologizes to her. Matt Cable comes back from the dead to give the couple his blessing. Elated, Abby runs up the courthouse steps to take her vows...only to see Swamp Thing get killed once again.
It also feels sad to notice the signs that Abby's fantasy isn't real, namely the gaudy colors and the replacement of plywood facades for buildings.