A monstrous creature lurking in the gotham sewers. said to actually been caught eating another human being. Killer croc is infected with the scarecrows fear venom, making whoever he bites suffer the illusions (assuming they'll survive him).
Batman: Gotham Knight
Killer Croc Injecting Batman with Fear Toxin.
Waylon Jones better known as Killer Croc, was born deformed. His parents dumped him into the Gotham Citysewers, where the chemicals transformed Waylon even more. The chemicals made him look like a Crocodile and gave him Super Strength and other Crocodile features. When Waylon was a young boy, Jonathan Crane (Scarecrow) used him as a test subject for his fear toxin. Crane pumped Waylan with so much toxin, that now he can inject fear when he bites a host. When Batman came looking for Scarecrow in Gotham's Sewer System to investigate strange kidnappings, Croc attacked Batman and injected him with the Fear toxin. Batman battled the monster and threw a Bat-Grenade in his mouth, this hurt Croc and made him run away; further into Gotham's sewers.
Unlike Anime, DC Comics Killer Croc has a different story origin. Waylon Jones was born with razor sharp teeth and a minor, however horrible disfigurement. Because of his odd appearance he was constantly bullied and tormented by older and more stronger children. Being called Croc; Because of how he looked. Year-after-year, Waylon was constantly bullied no matter what he did, good or bad. Eventually Waylon decided to fight, he almost killed his tormentors, however he was never bullied ever again. Because of almost murdering the boy, Waylon was sent to Reform School; which he hated a whole bunch. As years passed Waylon's body transformed also, making him look more and more like a monster.
Joining The Circus
On his 18th or 19th birthday, Waylon decided to become a cold-blooded-killer, saying that he was put on this earth be be a murderer. Because of this, Waylon was put in jail for a sentence of 20 years. After the sentence was over, a traveling circus wanted to hire Waylon as an Alligator wrestler.
Moving To Gotham
Waylon easily accepted the job, becoming loved by people all over the world. However, the murderous beast inside Waylon Jones emerged once again. After the circus closed down the Alligator wrestling, Waylon was sad and angry. Waylon left and made his way to Gotham City; where he decided to become a criminal kingpin. There was only one problem to this goal. Batman. Batman wouldn't let the strong hide creature take over Gotham. As Bruce was just beginning his career as Batman, he was still prepared to take on this adversary. Batman outsmarted Croc and sent him to Arkham Asylum for the mentally insane. Time and again, Croc has escaped and has tried to build his empire, however Batman has always been there to stop him!