Borderlands 2 - X Marks the Spot

It's time to find that treasure! This mission will begin after completing "Let there be Light".

Check the chests in the lighthouse and then find the chest near the window to the south. Stand just to the right of it and look out the window to find an outcropping of rocks below you with a large X on it. Jump down to complete the final "Message in a Bottle" mission.

Walk around and get back towards the elevator that will lead you back down below. Before going, you're going to be attacked by Scarlett's Crew. There are also going to be two of her lieutenants here as well. To advance the story, you need to kill both Lt. Hoffman and Lt. White. They aren't much different from the crew but they are taller and tougher. Lure the enemies back towards the lighthouse and pick them off one at a time. In fact, it's very possible that they won't follow you in if you need a quick rest.

With them dead, go near the elevator to find the Fast Travel station. Use it to get you to Wurmwater and then use the Catch-A-Ride station at the bottom of the ship. Take the ship to the area marked on your map and get close to the light. When you do so… you'll get swallowed. Just inside, you'll find a vending machine where you can grab ammo. I recommend that you do since you're likely low and you're coming to a couple of tough fights.

Roscoe

Continue further into the Leviathan and you'll find Roscoe! Roscoe is very similar to a Rakk Nest type monster encountered in the first Borderlands. The battle is much easier early on than it is later because over time, he'll create more and more Rakk that will harrass you. He will also spit acid blobs at you as his own direct form of attack. He is a little tougher than his predecessor from the previous game because the weakest point on his body are his eyes but they are covered up with blinders so it is much harder to find them.

Look for the black patches that cover his eyes and aim for those. You'll deal much more damage. Try to keep moving but watch out for the pools of acid on the ground. Try to leave as many Rakk in the air as you can without allowing them to become too much for your shields to handle because if you get downed, they will definitely be the easiest way to get back on your feet. Simply shooting into a crowd of Rakk will likely kill one of them.

With Roscoe dead, head towards the exit marked and the Leviathan will spit you out.

Leviathan

You'll have found the hidden treasure room of Captain Blade but you'll have to fight the Leviathan to open it up. I highly recommend fire based weapons, particularly a sniper rifle and rocket launcher if possible.

The fight will start with you on a platform staring at the gigantic Leviathan. You'll see that it has two large blue eyes on either side of its head, another large blue spot over where its heart might be and one last blue spot on its "tongue" which is actually a large Sand Worm and possibly the actual core of the leviathan creature.

The Leviathan has a few simple attacks. It can spray you with a strange liquid which attracts Sand Worms, spit a substance at you that deals damage and resembles slag but without the status effect and it can burrow into the cliff face and throw rocks at you. The Sand Worms that appear will be mostly normal Sand Worms but later on, you'll encounter at least two Sand Worm Queens.

The main strategy is to save your rockets and use conventional weapons to aim for the eyes and the heart. After dealing damage to each, that spot will burst and you won't be able to deal damage any more. I prefer going for the eyes first because they are harder to hit and that will be compounded by far more Sand Worms later on if you start with the heart.

As you kill the three different spots, more Sand Worms will appear. You can kill them if you like but try to leave a few if you can because if you get downed, you want to be able to use one to come back. This is why you are saving your rockets, because when you go down, you can pull out your Rocket Launcher and blast one of the worms to get back on your feet quickly.

When all three spots have been destroyed, the Leviathan will sit quietly and not attack in any way. It will wait until you've killed every Sand Worm there is. Kill them all and a couple of Sand Worm Queens will also appear. Once you've killed two of those, the Leviathan will return to attacking but after attacking, it will generally stretch out the Sand Worm "tongue" that it has, allowing you to easily shoot the blue spot on its underside. More Sand Worms may appear at this point as well, allowing you to use them for a Second Wind again.

After each attack, look straight up and get ready to attack the tongue. When it appears, try and get as many shots as you can. After a few rounds like this, you should burst the blue spot and kill the Leviathan.

The Treasure

With the Leviathan dead, you'll have to use it as a bridge to the treasure room. Climb onto the blade of the arm and then onto its back. This will lead you across the gorge to the far side. The doors will open in the distance. Go through the doors to enter the treasure room!

At this point, the credits will roll but if you wait through them or skip them, you'll be returned to the game and be sitting in the treasure room. You'll have to go around the right side of the pyramid and start climbing up by jumping from small block, to big block and then to the next level. Keep walking back and forth on this side of the pyramid and jumping up where you can to make to the top and a whole trove of treasure.

When you go to leave, you'll travel back along the ridge and it will take you back to a spot behind where you fought the Leviathan. You'll see a couple of vending machines on your left and the exit just beyond those. Before leaving, turn right and you should see a now opened gate that leads back to where you fought the Leviathan. Just near the gate on the right wall will be the second Hidden Vault Symbol for this area. Investigate that and then leave to return to Oasis. Talk to Shade to turn in the mission and finish the DLC!