Leaving from Zos Shivros Channel into Boreas Seabed (explorable), you will find Rion standing on the first level of the Halcyon. He will tell you to hold back the waves of Outcast raiders. Simply block the entry ramp with your party and take the waves as they come. Rion's crewmates will help you with the killing. This is one of the rare moments in the game where the combined numbers of your allies vastly outstrips that of your foes. This quest has large number of possible corpses to fuel Minion Masters and other corpse-oriented builds.