Nate fights his way across Navarro's ship, and after several shootouts, arrives at the platform where the helicopter has crashed. As Nate runs to help an unconscious Elena, Navarro appears out of hiding and shoots some nearby barrels. They explode, and Nate is knocked to the ground. His weapon is blown overboard by the blast. Unarmed, he takes cover as Navarro opens fire. When Navarro stops to reload, Nate takes his chance and engages Navarro in a fistfight. Nate eventually knocks an apparently unconscious Navarro to the ground.
He runs to help Elena out of the helicopter, and as she climbs out, she notices that Navarro is getting back to his feet, gun in hand. Nate notices that the cable connecting El Dorado to the helicopter is in a loose loop around Navarro's foot. Nate pushes the helicopter overboard, which plummets into the ocean below. Nate says his final words to Navarro, "Adiós, asshole," as the rope tightens around Navarro's ankle and pulls him and El Dorado, into the ocean.
Nate and Elena then discuss their experience, and Elena gives Drake back his ring, which she managed to save. As the two lean in for a kiss, they are interrupted by Sully. He reveals that he has brought with him a boat load of treasure, which Nate and Elena are happy to see. As they sail back to civilization, Elena reminds Nate that because she lost her camera, he still owes her a story. He smiles and assures her that he's "good for it".
First rule: Don't try to hit Navarro! You can't do anything to him yet.
The first shootout is Nate versus Navarro and three mercenaries. Navarro has a SAS-12 set to semi-auto that he will fire several times before getting a bead on you, and shooting you dead on if you are not in cover. The other mercenaries all carry M4s. Use the wooden boxes and the shipping containers on the right and left for cover. A reload for the SAS is propped up on one of the boxes right in front of you. The boxes can fall apart if they take too much damage. The recommended cover then is the shipping containers, especially the right one. Take aim at the two boxes Navarro is behind. Shoot them until they fall apart, carefully timing your shots to avoid Navarro's shotgun. Navarro will run off, allowing you to focus more on the mercenaries. There is a reload for the M4 propped up on the shipping container at the end of the area (it is recommended to exchange your SAS-12 for an M4 before leaving this area). When you are ready, jump over the box at the end, and quickly take cover.
There is no cover here besides the boxes, so you're on the clock. Another three mercenaries will be with Navarro. Repeat the previous strategy until Navarro's boxes collapse and he runs off again (coward). Then take care of the other mercenaries.
Again, pick up any ammo lying around and head to next area. Be aware of the falling crates and hit circle when prompted. Then continue on and take cover. Now it gets a bit harder. Notice that Navarro's boxes are now unbreakable. The thing to do here is eliminate the mercenaries one by one until Navarro runs up onto the big platform. Don't just rush up after him, though, because there will be a guy with a M79 grenade launcher that suddenly appears upon the railing of the big platform that Navarro ran up. Take him out, then go up.
(You may want to read this whole section before you do it.) Navarro gets in a cheap one. Duck into cover as soon as you can. This section is requires a precise set of actions. Wait for Navarro to lower his gun, and then quickly duck to the next set of boxes, and Navarro will destroy the set you were just behind. If you don't move fast enough after the second shot, you'll die. Wait for him to shoot twice again, jump to the next set, wait for him to shoot twice again, then rush up and punch him before he can do a follow-up shot. Quickly follow the quick-time event prompts that pop up. Once that's over with, Navarro drops his gun and he will knock you down. Quickly get back up and run over to him to punch him again, then follow the prompts one last time.