WARNING: The following contains spoilers for Justice League Dark #24, by Ram V, Amancay Nahuelpan, June Chung and Rob Leigh, available now.
In Justice League Dark #16, Floronic Man seemingly destroyed Swamp Thing by turning him into sludge, severely weakening the team. However, John Constantine hatched a plan that involved manipulating the Parliaments during a unique ritual to bring his friend back.
Now, with Alec Holland buried deep below the Green, Swamp Thing is dominant, charting a course forward with Abby Arcane, avatar of the Rot. In Justice League Dark #24, Swamp Thing has returned with a sinister upgrade that raises doubts as to whether he's friend or foe.
Bobo/Detective Chimp is trying to rally the JLD crew as he senses Wonder Woman isn't handling leadership well. Worse yet, Constantine is missing after messing with the Parliaments in Africa while Zatanna is self-destructing. Bobo ends up at Man-Bat's lab, but the doctor reveals he's busy experimenting with Swamp Thing's DNA, which shocks the detective. Man-Bat admits it's unethical, but he's stunned by what he's found. Swamp Thing is going through endosymbiosis, which means he has other external organisms within him. That's when Man-Bat confirms it could be he has other Parliaments working inside his genetics, potentially making him master of all Parliaments. Given that the Parliaments took power away from their guardians in the ritual, it's very intriguing.
Man-Bat further confirms Swamp Thing is rebuilding in familiar spots, fixing a darkness that lived beneath America. This takes him back to Rosewood, Illinois, where he once battled aquatic vampires that tried to spawn new monsters in a lake; as well as Kennescook in Maine, where he battled a primordial power that created a killer wolf. In other words, it's places where other creatures popped up that could rival him. He's also regenerating the swamp in Louisiana, his base where he's lived, loved and died time and time again. So it's an emotional rebuild as much as it's physical, leaving Bobo concerned.
As a student of science, Man-Bat is fascinated to hear the Parliaments are working together, now in balance, but using Swamp Thing as possibly the ultimate avatar will give him truly immeasurable power. Abby could also concede all the Rot to him, which seems to be the deal she struck with Constantine secretly in the last issue, making Swamp Thing a gateway to all the Parliaments. Floronic Man was also working with the Upside-Down Man from the Other Place to infect Earth, so there's a chance Constantine did this to make Alec the perfect mystical opposition to the ghoul. Still, it's possible Swamp Thing has been corrupted.
The Parliaments were disenchanted with Earth and how humans mistreated the planet. So if Swamp Thing loses his cool, he could literally purge the planet by having it turn on mankind. The Red, Rot, Green, etc. are what make up life, so Constantine placed a lot of trust in his comrade. Abby seems to be his moral compass and anchor for now, but if he gets out of control, Swamp Thing might betray the planet, making Constantine regret the choice.