Killer Croc is afflicted with what seems to be some form of regressive atavism, meaning he has inherited some of the traits of ancestral species of the human race. Over time the primal reptilian part of his brain gains more control of his psyche.
Regenerative Healing Factor
He has superhuman regenerative powers, able to heal even lost limbs.
His skin has hardened to the point where it is invulnerable to most forms of abrasion and even high caliber weapons fired from a distance.
He has grown so physically powerful and quick over the years that Batman has had to resort to planting explosive devices on Croc's chest to knock him unconscious. He has also been able to rip a large bank vault door right off its hinges with ease.
Croc has some experience at street fighting and wrestling, but he is nowhere near as proficient as Batman or Nightwing.
He harbors great rage against humanity, to the point were he could probably even operate a Red Lantern Ring.
Croc is an expert swimmer and can hold his breath far longer than normal humans.