Killer Croc was released a few months after Batman™ Fluxx to continue promoting it. It was given away in Game Trade Magazine (GTM) #200, which was distributed at GenCon, August 2016. Since it is specifically a Villain, it only works in Batman™ Fluxx.
As for all Creepers (Villains) in Batman™ Fluxx, it reads: "Immediately place + redraw. No one can win if you have this unless the Goal requires a Villain."