The MCU's Multiverse Saga has received mixed reviews from fans, with most of them leaning toward the negative end of the spectrum.
While I do agree that many projects that've come out since Avengers: Endgame haven't been as strong, I still have faith that the MCU will once again be on the right track. One way they could right themselves is by focusing on more of the supernatural characters that abound in Marvel Comics, and no other character would do that than the Macabre Man-Thing!
Who is Man-Thing?
Man-Thing first appeared in the Marvel Magazine Savage Tales #1 in May of 1971, and was created by Stan Lee, Roy Thomas, Gerry Conway, and Gray Morrow. Savage Tales was a line of black and white magazines that implemented a myriad of writers and artists to come up with stories with various characters that were established, such as Conan the Barbarian, behind-the-scenes facts about films, culture, etc., and introduced new characters and concepts to the line, such is the case with Man-Thing. Throughout the 1970's Marvel in particular wanted to cash in on the horror craze that was going on in pop culture at the time, so they created a bunch of horror comics and magazines to pull in more readers, with Savage Tales being one of them.
As for Man-Thing, he was once a scientist named Ted Sallis who was working on a new version of the famed super soldier serum that was used to create Captain America. Due to the secrecy needed for such a project, Sallis went to the Florida Everglades to conduct his work away from prying eyes, but he brought his wife, Ellen Brandt, along with him, a choice he'll regret for the rest of his days.
After months in the swamp, Sallis managed to cook up an untested version of the formula but was soon betrayed by Ellen who sold him out to members of A.I.M. (Advanced Idea Mechanics) who wanted the formula for their own evil purposes. Managing to flee, Sallis tried to escape in a car in which Ellen and the A.I.M. agents followed, but seeing only one option, Sallis injected the formula into himself in order to hopefully fight off his pursuers.
Unfortunately, Sallis careened his car into the swamp, which would change the course of his life forever. There were magic properties within the fetid swamp water, and combined with the formula, Sallis became the creature that would soon be known as Man-Thing. Emerging from the murky depths, the swamp creature saw the A.I.M. agents as well as Ellen and attacked them. Killing the agents, Ellen was the last one standing, but Man-Thing touched her face which proceeded to burn her flesh. Ellen fled in pain and terror from the monster, and with his fate now tied to the swamp that birthed him, Man-Thing went deep into the Everglades, his new home.
Over the course of Man-Thing's early years, his powers and abilities would be expanded and added upon, such as being able to burn people and beings if they are afraid by touching them (like he did with Ellen in his debut), but one thing about Man-Thing that I want to point out is that once Ted Sallis was transformed into the swamp creature, Sallis basically disappeared on a subconscious level. In other words, Man-Thing doesn't have any human intellect or even the mind of Ted Sallis, he's more akin to a walking mound of swamp gunk, without any desires or emotions of his own. Essentially, he's an animal, but this animal can sense strong emotions from people and creatures around him when those people and creatures emit them.
Writer Steve Gerber took the Man-Thing character and established much of the lore and powers I just mentioned, in particular Man-Thing's connection to the Multiverse.
Why Man-Thing would fit perfectly in MCU Multiverse Saga
During Steve Gerber's now acclaimed run on Man-Thing, it was revealed that Man-Thing is more than just a mindless monster, he's the Guardian of the Nexus of all Realities. Chosen by god-like beings, Man-Thing was created as a means to safeguard the Nexus, which is a gateway to an infinite number of realities that stretch across time and space, and the location of the Nexus is in the swamps where Man-Thing was first created.
I think Man-Thing could be a crucial part of the Multiverse Saga mainly because of his connection to the Nexus of all Realties, and since Man-Thing has already appeared in the Werewolf by Night Special in 2022, (albeit with the change that he's aware of his human identity and is intelligent) and with rumors that a sequel to the special will be coming out, it's possible that audiences will be seeing more of the horror/supernatural side of the MCU sooner rather than later, in particular Jack Russel as Werewolf by Night and in particular Man-Thing.