Gunrunner

You have to find and destroy all of Penguin's weapon caches. Nightwing will provide you intel about Penguin's weapon delivery vans. Head to the van's location, track the vehicle and spook them. When they try to lose you, head to the rooftops and track them. Keep following them until they reach the Sionis Industries building near the Falcone Shipping Antenna in Bleake Island.

Head inside the building through the side door and hack the console on the other side of the wall using RHD to open the main gate. Remote control the Batmobile and take out the auto-turrets. Find the grate where you can grapple up then operate switch to open the roof covers.

Head to the roof and smash the windows. Once you drop below, beat down the thugs with Nightwing's help. Like before, set the explosive gel on the weapon crates inside the vault then detonate them.

The second intel will become available after you blow up the missile launcher in Founders' Island. Head to the location of the truck and fire your tracker ammo. Next, knock on the truck or call in your Batmobile to scare them. Follow them by gliding from roof to roof until they lead you to one of Penguin's weapon caches.

Take out the guard outside the building and enter through the door. Enter the vent nearby then make your way to the cracked wall. Place an explosive gel there, then return to the vent. Get into position behind the two hostiles, detonate the charge then take out the guys nearest to you at the same time. This should knock out all of the men in the room.

Now use the Bat Claw to pull the grate covering the vent near the ceiling and continue there to find the main weapons cache. Use the disruptor to disable the nearby weapon crate and two of the armed guards. Get into position and use Multi-Fear takedown to whittle their numbers quickly. Detonate the weapons inside the vault to complete this mission.

This intel becomes available after Harley Quinn's appearance in the main story. Head to the marked location of the weapon truck in the map then spook the goons, either by knocking at the back of the truck or arriving via the Batmobile. You have to trail them by gliding on the roof until they reach the weapon cache location in the water filtration plant in Bleake Island. Examine the gate where the truck entered so Alfred can give you the location in the tunnel.

Follow the line leading you to the sewers. There are armed guards there so it will be easier to take them out using the Batmobile's weapon. Head to the room above to find the electric box controlling the barricade below. Pull the lever down and pick up the Riddler Trophy on the table along the way.

Enter the Batmobile and use the power winch to pull the hanging weight to lift the heavy gate. Get inside The Shaft and position yourself for a Fear Multi-takedown. There are only three grates in the ceiling where you can enter and there are no armed guards inside, except for a blade-weilding brute.

After eliminating the guards inside, set the explosives in the weapon crates and close the vault door. Detonate it afterward. A cutscene will trigger and you'll discover that Nightwing has been captured. Head to Penguin's location to rescue him.

Head to the rooftop and check the area. You can't use your detective mode in this area since there's a strong jamming signal from one of the guards there. If you manage to take out the thug with a backpack, you'll be able to use Detective Mode once again. First, get to a vantage point and take out the sniper first. After eliminating all guards in the rooftop, access the fusebox to open the elevator gate. Drop down until you see Nightwing and the guards surrounding him.

You need to find a way inside and make a surprise entry. Find an opening on the wall where you can crawl in. There's a sentry gun in the next hallway. Disable it with your RHD and destroy it. Open the vent grate and crawl in there. Follow the vent so you can get inside the weak wall behind Nightwing to rescue him.

After beating all the goons, set some explosives inside the crate and close the vault door. Penguin will take Nightwing hostage shortly. Perform a dual team takedown and detonate the explosives to destroy the last cache. Now you have to bring Penguin to GCPD lockup to complete this mission and close the case.