Part way through the DLC you will unlock a side mission called "Alan Smithee's Treasure Ocean." It is located towards the northern part of the DLC map. There is a yellow sub with the blue side mission icon above it. Once you start the guy offers you to collect some treasure so he can finance his movie. The reward for completing is: $10,000 and 5000 Overcharge.
First things first, you have to collect three shipping charts. Fast travel to the main island and collect the 3 that are highlighted by blue spots on your map. One his half way up the lighthouse. Use the bush to jump up to the rail and grind around it until you see the shipping chart. Another one is located on the south side behind a building on a little island with a stranded boat washed up on it. The final one is located on another island. There is an "X" on the south side of the island. When you hit the
button to dig it up, a berserker pops out. Kill it and it drops the last shipping chart, collect the last one.
Fast travel back to the "Flotsam" which is located left of where you started the mission. Swim to the way point and he will then have you swim to the island to the North East of where you just were. When you deliver the charts, sunken ships covered in treasure will rise from the water.
Now you have to collect $500,000,000 in treasure. While collecting the money by smashing the crates, opening the chest and collecting artifacts in the highlighted areas. wingers will start to attack and "steal" the money. They can flee the area with the treasure they stole if you don't kill them in time. They got away from me three times but I was still able to collect enough treasure to reach $500,000,000 so it is not necessary to kill them. After you collect the $500,000,000 you have to bring it back to the sub. Wingers attack, I chose to just go right by them and head straight to the sub. Press
to get into the sub and a cut scene happens. At the end of it the "SUCCESS!" screen pops along with your achievement!