The Dark Knight Returns
This gang appears in The Dark Knight Returns version of Gotham City (Earth-31).
After their leader was defeated and humiliated by Batman, some members went on to form a group of vigilantes called the Sons of the Batman.
Mainstream DC Universe
The Mutant gang have begun appearing in current DC titles, such as Batman, Inc and All-Star Western suggesting they will become a dominant gang sometime in the future.
The New Batman Adventures
The Gang appear in the episode "Legends of the Dark Knight" which adapts a section of The Dark Knight Returns.
Two members of the mutant gang can be seen in the future set episode "How Long is Forever?"
Batman: The Brave and the Bold
They also appear in the future set episode "The Knights of Tomorrow".
Batman: The Dark Knight Returns Part 1 & 2
The gang appears in the DC Animated DVD adaptation of The Dark Knight Returns.
Alfred Pennyworth and a young Bruce Wayne encounter a gang called The Mutants in the second season episode "This Ball Of Mud And Meanness"