Your fight against the Killer Croc will be your first actual boss fight in Batman: Arkham Origins. It’s a fairly easy fight and can be completed in a matter of minutes if played out correctly.
The fight starts out after a cutscene in which Killer Croc tosses a fuel tank towards you which you evade and then begin the fight. Your primary way of inflicting damage onto him is by stunning and giving him a beat-down so you should go in for this whenever you see an opening.
Killer Croc doesn’t have much up his sleeve so throughout the the battle, he mostly uses his one attack where he runs at you while trying to slash you with his claws. This attack is indicated through a red prompt, and you can easily dodge it using the evade mechanic.
Killer Croc will also try to grab you, this can also be evaded, but if you happen to mess up and get grabbed, rapidly tap the escape key until you have broken free of him.
Over the course of the fight, Killer Croc’s thugs will also enter the arena via a helicopter and when they enter, Killer Croc will also pick up one of the fuel tanks in the arena to throw at you.
When he’s holding up the fuel tank, you can easily make it backfire on him by quick-firing batarangs on him, which will cause the fuel tank to blow up and deal massive damage to the Croc.
There’s nothing more to this fight so just rinse and repeat the stun and beat-down method until you’re through with the Croc. The boss fight concludes with a cut-scene where batman is asking for information on who hired the Croc and the Croc telling him the intentions of the Black Mask’s Assassins.