This is the first appearance of Mumbo and Fixit. Both characters were voiced by Tom Kenny and both were created specifically for this show and have not appeared in the mainstream comics.
Fixit was originally perceived as Psimon, a vicious criminal with psychic abilities from the Teen Titans comic book.
The scene when Cyborg gets hit with a baseball and a kid with a prosthetic hand, who marvels at Cyborg's metal prosthetics, retrieves it is taken from "The New Teen Titans" (vol.1) #8.
Robin's mask is seen off his face when Cyborg pulls him.
When Beast Boy is counting seconds, he counts in "Gotham Cities" (1 Gotham City, 2 Gotham City, etc).