MISSION 22 - The Siege of GCPD
Objective: Meet with Oracle at GCPD to analyze the data for leads about where Scarecrow has taken Gordon
Now that the Clock Tower computers are under Oracle's control once again, glide or swerve your way through the streets to arrive at the GCPD lockup. When you arrive, you'll find Oracle in one of the rooms at the back of the maximum security area. Talk to her to start things off with a scene.
Main Objective: Stop the assault on GCPD
Ignore the raining debris and flashing red strobe lights as you backtrack to the garage where you just parked. As you walk into the garage, you'll find the Batmobile missing and a pair of APCs will swing into view, disgorging a large number of militia enemies. As usual, your first priority should be the healing and electrifying medic. After that it's up to you who to take down as there are multiple cattle prod wielding enemies, shielded foes and militia with other melee weapons.
Remember to use your quickfire gadgets to deal with the enemies using electricity and take advantage of any fallen weapons you can pick up to make the fight a bit easier. Also by now the aerial attack combo should be ingrained in your mind for dealing with shielded enemies (B + AA + X/ Circle + XX + Square). You can also use Batmobile assisted takedowns here if you get your combo up high enough.
Objective: Investigate power generator to restore power to GCPD
When the last militia enemy goes down, you will contact Cash to attempt to get outside. No dice, I'm afraid. As you may have already noticed (due to the lack of lighting) the power is out. Oracle will notify you of a backup generator outside the building. Flutter into the Batmobile and look for a large exhaust fan above and to the left of the entry doors you just came through. Use the Power winch and a serious revs to rip it out of the way.
Grapple up to the ledge where the fan was and step into the tunnel beyond. At the end of the short tunnel, look to your left to find a duct you can grapple up to. Follow the duct until you reach a cover at the end that you need to remove. Drop down and walk through the open doorway here to find yourself in a large shaft leading upwards. You should be able to grapple all the way up to a small space at the top.
Sneak along the duct until you can finally emerge from a grate at the far end into one of the upper offices of the GCPD building. A balcony will be overlooking the carnage going on below. After the scene with the onrushing drone army ends, you'll regain control on a girder overlooking the drones below. Grapple up to the top of the roof and then glide down to the West side of the building where the marker is pointing to the backup generator.
Objective: Access GCPD parking garage to power up the backup generators
How many backup generators have they got in this damn place? Walk over to the railing overlooking the garage entrance to see a dragon drone guarding it. Blind the drone's optics with the Remote Hacking Device before dropping down and crouching under the door. A second or two after you pass under, the door will slam shut behind you. You'll see the marker pointing to the generators ahead of you, but a group of militia will be standing in your way.
If you are quick, you can use the Disruptor to disable the cattle prods of two of the enemies before the group rushes you. You'll be dealing with a shielded bruiser, two cattle prod militia, one militia with a pipe and six regular militia. Quickfire REC gun is your friend here. Quickly use it on the two cattle prod militia and then focus all your efforts on bringing down the shielded bruiser. Getting rid of him quickly will make the fight much easier.
After the goons are in dreamland, approach the generators. All they need is a quick zap with the REC gun. Do so and they will be humming away merrily once more. After the power is restored, you can continue dealing with the primary objective.
Get in the Batmobile and ready yourself. If you are ever going to upgrade the Batmobile, now is the time as this is the last major fight it will be in story-wise (it will still be in large fights in the sidequests though). When you are ready, emerge from the garage to meet the drone army outside. You'll roll out against a force of sixty various types of drones.
Immediately start by blowing up the dragon drone over your head, then start firing on the missile launching drones. You'll see circles begin appearing on the tanks showing Oracle attempting to hack or disable them (hack = purple, disable = green). You can use these sudden shifts to your advantage by firing on the disabled tanks and leaving the hacked tanks to wreak havoc among the enemy line.
You should have the level 4 missile barrage ability by now (and hopefully have the upgrade that prevents overdrive loss), store up to level 4 as often as you can to take down ten drones in a single barrage. Don't forget your EMP as well if you are in a tight spot. The main thing here (as you'll see in the video is keeping your back to a wall/ impassable area to prevent getting surrounded. If too many drones circle you, you are essentially screwed unless you have godlike reflexes.
Objective: Stop militia from disabling the GCPD security systems
After the army is scrap metal littered across the streets, a scene will play out showing that the fight isn't over yet. When you regain control, grapple up onto the rooftop of the GCPD building to find an infiltration squad waiting for you. Note the glowing (electrified) fence here. During the fight on the rooftop, Oracle will trigger various objects, allowing you to use them as environmental takedowns. This can make your battle a whole lot simpler if you remember to use them.
The first wave of enemies consists of seven regular militia (one with a pipe), a pair of shielded militia and a bruiser. Try to get the hang of the environmental takedowns if you can during this fight. Stun and beatdown the bruiser first if you can to avoid his cheap damage shots. Follow it up with an aerial combo on the shielded militia and then go to town on the remaining enemies. When only a couple are left, another wave will touch down and join the fight in progress.
Four ninjas, a medic and three regular militia will add to your woes as you continue the abruptly extended battle. Get that medic quick as having multiple electrified enemies on the field causes rapid death. After that, you can deal with the enemies in your own fashion, just being careful to avoid the quick blindside attacks of the ninjas. Hopefully you haven't exhausted all your health as the fight has only just started (don't worry, when the scene triggers so does a checkpoint).
After the arrival of the multi-type bruisers who are flanked by four regular militia and two medics, the fun really starts. You will need to adjust your dodging and counterattacks on the fly as they switch modes. This will really test your observation and reaction skills. Take advantage of any oracle assisted takedowns you can (there are more on the other side of the helipad) while you deal with these dangerous foes.
As always, get rid of the medics first. Then focus on the multi-type bruisers. Two of these guys trying to attack at once is a nightmare. Take at least one out fast if you plan to survive. Once the final militia member falls to the floor, the battle for the GCPD lockup will end and you will emerge victorious.