Right after the fight with Killer Croc starts, focus mainly on avoiding his attacks (lean the analog stick to the side and double-tap the button displayed by the game.) thanks to which you will not be taking damage resulting from the enemy's strong attacks (the screenshot).
Right after Killer Croc performs an attack that does not connect, run up to him and implement the same strategy as in the case of the armored enemies. You need to stun the boss with the cape and lunch a series of quick attacks afterwards (the screenshot). once the series of your attacks finishes, jump away from the Killer Croc again and do not allow him to take over the initiative.
On the rooftop, there will soon appear the first group of mercenaries, who will be obstructing you from weakening Killer Croc. Ignore them for a moment and note that the boss picked up a fuel tank. Try to hit the tank with a batarang, either by quick throwing the gadget or by aiming at the tank beforehand. If you are not quick enough, try at least to avoid the explosion to avoid taking damage.
Sooner or later, you still need to get rid of the mercenaries anyways but, the best strategy here is to rely on Killer Croc's blows and hope that they will be weakening and killing the other enemies. Start launching direct attacks only after the boss tries to pull himself together after a failed attack, and do not exaggerate with their intensity.
The next part of the fight with Croc is similar to the previous one. So, you need to stun the boss with your cape and inflict damage, as well as to explode the tanks that he lifts and watch out for his helpers. The only new thing now is that you will have to defend yourself from Croc's bites after a series of blows that you land. The solution to this problem is tapping rhythmically the action key/button, until Batman liberates himself.
Finally, Killer Croc will grab one more tank and to deal finally with the boss, you need to throw the batarang at the tank for the last time. Watch the cutscene, after which you will be automatically transported to the Batcave.
[New Character Trophy: Killer Croc]
[New Concept Art: Killer Croc]