The Great Hunt

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

Detailed walkthrough
Upon speaking with the Mariner, she will describe a mysterious creature that has been destroying boats attempting to leave and arriving in Far Harbor. She asks the Sole Survivor to accompany her to face the mythical beast. The Mariner takes her leave and the player character attempts to do the same but is stopped by Avery, who warns the Sole Survivor that it is an old myth and they are wasting time and putting themselves in unnecessary danger. One will then board the boat and travel to Red Death Island.

Once arriving, the player character will begin the search for Red Death. After a short conversation with the Mariner, the Sole Survivor will discover the monster of legend is in actuality, a tiny bloodrage mirelurk. After defeating the mirelurk, speaking to the Mariner will reveal her disappointment.

Despite the outcome, the Mariner will still reward the Sole Survivor with the Legend of the Harbor, a unique version of the fisherman's outfit. She will ask for the Sole Survivor's advice on what to tell the townspeople. The available suggestions are telling the truth, embellishing the tale to make it sound more impressive, or saying that the Red Death simply could not be found. Whatever is recommended, the Mariner will agree to go along with it.

Upon returning to Far Harbor, the player character will receive a hero's welcome from the townspeople, depending on their decision on what story to tell. If the player character encourages the Mariner to tell the truth, the townspeople will jeer and mock her. If one chooses to embellish the tale, the townspeople will be in awe of her. If the Mariner says they couldn't find the Red Death, the townspeople will be mildly disappointed, but also comment that it's probably for the best as "if you did find the Red Death, you'd be goners for sure".

Bugs

 * Completing the main DLC questline may cause this quest to become unavailable.
 * The only known fix is to reload a save from before completing the main questline. The quest can also be started with the console command.
 * When traveling to Red Death Island it is possible getting a black screen but still being able to move, but landing in water. To fix this one must activate V.A.T.S. (travel to the destination and target the Red Death in V.A.T.S., or hold down the V.A.T.S. activation button). Toggle console command on the PC to see, toggle  again to target.
 * Possibly related to the above glitch, the player's boat may disappear, but the prompt to activate the boat's controls will still appear just off the northeastern coast of Red Death Island. The boat will be entirely invisible. Objects can still collide with the boat and it is not possible to fast travel after activating the controls to return to the docks of Far Harbor. Use your best pixel-hunting skills to activate the quest marker which will trigger the returning sequence. After a few seconds, the screen will fade to black and you'll find yourself on a boat returning to Far Harbor.
 * After the boat pulls away from the dock and the game starts a loading screen, one may be dropped in the ocean without the boat near the target island. Opening the console and typing will move the player character to the correct location, but the boat will still not be present. To return to Far Harbor, the quest marker points to an activator floating in mid-air where the boat should be. Activate it and wait a moment and the player character will load on the boat as it arrives back in Far Harbor.
 * Regardless of whether the subtitles are turned on in the game settings, there are no captions for the Mariner's radio transmissions during the boat trip.
 * The quest may get stuck at the last objective after leaving the boat back in Far Harbor. The crowd will still gather and try to initiate dialogue, but the Mariner will not answer and repeat the same sentence if tried to talk to.
 * The only way to proceed at that point is ending the quest via console commands like or