Killer Croc is a man affilicted with a disease that mutated him into a reptile. Sporting an iron jaw, Croc is a physical powerhouse. He became a constant foe of Batman and his partners. Killer Croc and Cheetah escaped Arkham Asylum and went on a crime spree together. At some point, they were recruited by the Penguin to join his Animilitia team. About three months after his escape, Killer Croc robbed the Central City Copper Quarry. The Flash began tracking Croc's movements. The next week, in Gotham City, Croc joined Cheetah at the Jewelry Store by tunneling through the floor. He took on Nightwing and prompted Cheetah to finish the mission. Unable to take on Croc alone, Nightwing triggered the store's alarm. The Flash responded. Croc took out Flash and fled the scene. Nightwing uploaded footage of the battle to Batman's subnet. Batman noted the copper quarry wasn't Croc's usual M.O. but Nightwing brushed it off as the Midas Heart making everyone crazy.
At the Gotham Zoo break-in, Killer Croc entered the reptile house in hopes of Batman following. Green Arrow came instead. Arrow's attacks did little against Croc's impervious skin and he soon charged the hero. Croc broke out a net arrow and tied Green Arrow up in the remnants. Somehow, Arrow used only his feet and mouth to draw his bow and shoot a knockout gas arrow right into Croc's mouth. Croc passed out and landed on top of Arrow. After Man-Bat freed everyone, Croc hitched a ride with him and fled the scene. At Bumbershoot Mechanics, Croc and Nightwing had a rematch. Nightwing was too agile and dodged Croc's attacks until Penguin tasered him. Croc threw Nightwing out a window. The Flash arrived on scene, ran up the side of the building, and saved Nightwing. Croc flew off with Penguin using his trick umbrella. At the Aviary, Croc helped finish building the tractor beam console and fired on the Midas Heart asteroid. The hacked Blade Wolf and Tiger Claw made short work of Croc. While being loaded into a police van, Croc lamented the terrible food that awaited him.
Red Robin and Nightwing pursued Killer Croc in sector 12. After Nightwing tasered him, Croc ran and found a manhole cover. He tossed it at the heroes and descended into the sewers. While Red Robin and Nightwing were overwhelmed by the stench, two crocodiles dove at them from behind. Croc's trap fell apart once Batman burst through a wall and knocked out the beasts. He supplied Nightwing and Red Robin breather masks. Red Robin tossed smoke screen balls at Croc then Nightwing took off and knocked Croc out with a running flying kick.