Delphinian Swamp is a quest available after the quests of Banshee Wetlands have been completed. It can be done once the player has reached Lvl. 32 and unlocked Delphinian Swamp dungeon, although it may appear in the quest list before the dungeon is unlocked.
To complete the quest, Delphinian Swamp needs to be passed, that means the end boss needs to be defeated.
Click on [Campaign] -> Select [Delphinian Swamp] -> Gain passage through the dungeon The Delphinian Swamp is the darkest area in the whole swamp. You need peerless courage and strength to get through it alive.