While seeing the continuing adventures of the mutants would be a lot of fun, both a series and a sequel will need some solid antagonists to keep the turtles on their toes. The mid-credits scene of "Mutant Mayhem" shows Cynthia Utrom (Maya Rudolph) keeping tabs on the brothers while telling a subordinate to get the Shredder involved. Therefore, the show or sequel will introduce Shredder in a greater capacity than merely looking at his backside. Shredder is the best-known villain in "Teenage Mutant Ninja Turtles," so the franchise could utilize him in many ways.
There's also the matter of Cynthia herself. Her last name, "Utrom," typically refers to the race of brain-like aliens in the franchise most often associated with Krang. It's possible "Mutant Mayhem" will change Krang's origins or turn Cynthia into a variation of Krang to give the turtles a run for their money. Her glasses are also very Krang-like, so that's another tease the franchise likely has a lot in store for her moving forward.
There's also the issue with Bebop (Seth Rogen) and Rocksteady (John Cena). Usually, they're henchmen for Shredder in "TMNT" properties. But by the film's end, they're living in the sewer and getting along with the turtles. There's always a chance Shredder could recruit them in a sequel or series to work for him. After all, they worked for Superfly (Ice Cube) initially, and it didn't take much convincing to get them to swap sides. It could easily happen again, much to the turtles' chagrin.
"Mutant Mayhem" lays the groundwork for plenty of stories to come. And fans would no doubt be delighted to spend more time with these iterations of the beloved characters.
