However, Baxter also appears in the film, voiced by Giancarlo Esposito, making Superfly a new and separate character.

Source: https://screenrant.com/tmnt-mutant-mayhem-shredder-not-villain-why-director/

Things get complicated, though, when their first major villain, Superfly (Ice Cube), is a mutant just like them.

Source: https://www.themarysue.com/teenage-mutant-ninja-turtles-mutant-mayhem-post-credits-scene-explodes-with-turtle-power/

This film will see Leonardo, Donatello, Raphael, and Michelangelo meet their soon-to-be partner-in-crime April O’Neil as a new mutant threat lead by the villain Superfly emerges in New York City.

Source: https://collider.com/teenage-mutant-ninja-turtles-mutant-mayhem-tickets-on-sale/