In the comics, Slade's supervillain name is "Deathstroke." This name has never been used in a Teen Titans cartoon, because it was decided that a character with "Death" as part of his name should not be in a children's cartoon. However, he was referred to as Deathstroke in Lego DC Comics Super Heroes: The Flash (2018), an animated movie marketed to children, which was released a few months before this movie.
The Challengers of the Unknown is a team of DC Comics characters created by Marvel Comics co-creator Jack Kirby in 1957. The basic premise of their series as a team of explorers of the alien and unusual who felt they were living on borrowed time after miraculously surviving a plane crash, predates the later Marvel Comics creation, The Fantastic Four, also co-created by Kirby as well as Stan Lee, in many respects.
A montage of flipping comic pages from the "The New Teen Titans" comic (#1, November 1980) appears at the beginning of the film. This is also a reference to Marvel Studios' flipping comic pages logo.
Khary Payton is listed among the contacts on Cyborg's phone. That's the name of the actor who voices Cyborg.