The moment you go into this fight Killer Croc will charge at you. You will need to dodge out the way of his charges. Once he has charged at you a couple of times you will need to stun him using your bat cape and then punch him constantly whilst he is stunned.
When you have finished this combo on him you will need to dodge to miss his attack. He will then try to throw one of them at you just after some enemies drop in by helicopter. Just before he throws this barrel at you throw your batarangs at the barrel to make it explode and cause some damage to Killer Croc.
Now you will need to fight Killer Croc whilst defendin yourself from the two enemies that try and attack you. Do this by dodgeing Killer Croc when he charges and use the counter when the blue halo appears above the enemy’s head. Proceed to stun the enemies using your batcape and stun Killer Croc in the process. When killer croc is stunned punch him a few times to take off more of his health. Continue doing this until Killer Croc tries to bite you.
When killer croc tries to bite you mash the displayed button to get yourself out of it, then proceed to imediatly dodge the next atack from Killer Croc. Killer Croc will then go to the corner to grab another barrel to throw at you. Three enemies will drop in to attack you whilst Killer Croc grabs a barrel. throw your batarangs at the barrel before these three get to you.
When the barrel gets destroyed do the exact same thing you did just before when there were two enemies. Dodge when Killer Croc charges at you and stun using the batcape.
Killer Croc will try and bite you one last time after this. Mash the button displayed to get through the next part. When Killer croc goes for the last barrel just throw your batarangs at it and you will have defeated killer croc.