The Great Hunt

The Great Hunt is a quest in the Far Harbor add-on for Fallout 4.

Detailed walkthrough

 * The Mariner will tell about a mysterious creature that has been destroying boats leaving and coming into Far Harbor.
 * She will then ask to go to the boat and she will go to hers. Before boaring on, the player character is stopped by Avery, who tells it is an old myth and the player character is wasting time and putting themselves in danger.
 * The Sole Survivor will then board on the boat which has already been programmed by The Mariner to go to Red Death Island.
 * Once arriving, the player character has to look for the Red Death.
 * Talk with The Mariner about finding Red Death, and then it will appear in front of them.
 * Vanquish the Red Death (takes 1 or 2 hits).
 * The Mariner will be very disappointed, but will still reward with the Legend of the Harbor, a unique version of the Fisherman's outfit. She will ask if the Sole Survivor wants to tell the truth about the monster or lie. One will then get back onto the boat and sail back to Far Harbor.
 * The player character will then receive a hero's welcome from the town's people depending on if choosing to lie or not.

Bugs
When travelling to Red Death Island it's possible that one will get a black screen but still be able to move, but the Sole Survivor will land in water. To fix this one must target something in Vault-Tec Assisted Targeting System (travel to the destination and target the Red Death in V.A.T.S.)