Unlike the Killer Croc boss fight in Origins, his encounter in Batman: Arkham Asylum is pretty underwhelming, to say the least.
Do not get your hopes up after your first meeting because despite how Killer Croc appears in the game, you will only be trying to run away from him while searching for a story-related item in the sewers.
This is the one and only encounter with Killer Croc in the game. There will be no opportunity to land your punches on him.
Killer Croc’s lair location in Batman: Arkham Asylum
Given his huge size, strength, and insanely sharp teeth and claws, Killer Croc was placed in a special cell underneath Arkham Asylum, inside the sewer system. After Batman’s chat with Poison Ivy regarding the anti-venom for the Titan formula, she sends him down to the sewers.
You can start by heading towards the crashed elevator in Intensive Treatment. Search for the control panel using Detective Vision to clear the path down for yourself; head on down and deal with the thugs before entering the gateway to the sewers.
On your way down through Intensive Treatment, you will face the Scarecrow, after which he gets chased into the sewers threatening to dump his fear toxin in the water. During this conversation, Killer Croc appears and takes Scarecrow underwater, leading to his ‘apparent’ death.
At this point Batman will be using his scanner to track the location of the cure identified by Poison Ivy, this will lead him straight to Killer Croc’s lair.
How to beat Killer Croc in Batman: Arkham Asylum
Use your Line Launcher to reach the entrance to Killer Croc’s lair and walk past the open iron gate. Batman will automatically place a radio beacon and some Explosive Gel on the floor. This is your escape plan, which we will get to later.
Killer Croc’s lair is an old sewer network that is designed like a maze in Batman: Arkham Asylum. You, however, do not have to worry about finding your way out. The only thing you need to keep an eye on is your newly tuned scanner on the left side of the screen. It will lead you straight to each plant spore that Poison Ivy wants.
You need to crouch your way through this entire level.
The most important thing that you need to know while collecting the spores is to not make any noise. You need to crouch while moving across the wooden platforms to remain in stealth. If you sprint or make too much noise, Killer Croc will sense your presence and come after you.
That being said, he will sometimes start destroying wooden platforms from below at random. When that happens, start running until he stops. If you keep on running after that, he will jump atop one of the platforms and start chasing you.
The only way to stop him from chasing you is to hit his electric collar with a Batarang. This will cause him to fall into the water and reset the boss fight. Keep on repeating this till you have collected all the spores.
It is important to note that on hard difficulty the only difference is the frequency at which he jumps out of the water. This actually makes this section easier as it gives you more time to run through the maze by keeping on hitting his electric collar, instead of silently moving around.
After collecting all the plant spores, Batman will activate the beacon he left at the entrance. You can now find your way back by following the single.
During this sequence though, Killer Cros will keep chasing you until the end. Make sure to jump each gate and use your Line Launcher where there are no wooden platforms. When Killer Croc jumps out of the water, quick-fire a Batarang to throw him back in.
When you finally reach the exit, the iron gate will be closed. Quickly turn around and detonate the Explosive Gel (remember your escape plan?) to send Killer Croc falling. This is how you get past him in this little boss encounter in the game.