The Mutants are street gang members whose criminal activity takes place in Gotham City .
Most of them seem to be bald, indicating that they have shaved their hair off. They also wear leather uniforms and visors, covering their eyes.
Powers and Abilities
They don't seem to possess any super powers. They are also able to fight in a hand to hand combat but most of the times they are easily defeated.
In Gotham City, a member of the Mutants street gang races through a sewer on a motorcycle, fleeing from a robbery. An armored arm juts out and clotheslines the gang member off of the bike. He cowers as he finds himself before the Batman. Using a small Bat-taser, the Dark Knight incapacitates the gang member and radios to Nightwing in a separate tunnel for a report. The sidekick quips about using the handlebars from another motorcycle as she takes out two more Mutants.
Batman and Nightwing are just finishing off some members of the Mutants, when suddenly Nightwing notices the bright light on the sky, thinking that it's just a storm but Batman says it is not, while he is watching them making a beeline for Arkham Asylum.
In the comics
This gang, also known as "Mutant Punks", appears in The Dark Knight Returns version of Gotham City. The Mutants differentiate themselves from mainstream society with a brand of slang and a distinctive look, based on visors, mohawks and jackboots.
The leader of the Mutants gang is nasty, brutal, and feral. He doesn't act like a civilized human. He defeats Batman in their first encounter, a hand-to-hand battle at the garbage dump. The Mutant leader ends up in custody though. Once in custody, the mayor decides to have a one-on-one conversation with him. The Mutant leader proceeds to rip the mayor's throat out with his teeth, chuckling as he does it. Batman tricks him into breaking out of his cell and following a vent out of the jail. He does not know that Batman is waiting to fight him with his entire gang watching. Batman ultimately defeats him and ends the reign of the Mutants gang on Gotham.
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".
Since then they have appeared in the mainstream DC continuity, being featured in 2010 Batgirl series.
Recently they made their debut in the New 52 appearing in Batman, Incorporated. Shortly after the Night of the Owls, the Mutants were part of a Gotham-based Leviathan smuggling operation, but were taken down by Batman Inc. They later appeared in All-Star Western suggesting they have become a dominant gang in Gotham City.