This achievement can be unlocked postgame, after defeating the final boss. Spoilers ahead:
*** Spoiler - click to reveal ***Return to the Hall of Doors, where you fought the final boss. The Rusty Belltower Key will be on the floor. Pick up this key and return to the Lost Cemetary - near the area where Death's Door used to be, there is a locked gate blocking the belltower. Use the key to unlock the gate, then climb up to the bell. Hit the bell to turn day into night-time - this is necessary for most postgame content to unlock the true ending.
*** Spoiler - click to reveal ***Once it is nighttime, return to the Stranded Sailor. For this bit you need to have the Ink-Covered Teddy Bear - this is a Shiny Item located nearby, South of the Stranded Sailor. Use your hookshot to cross the water, where you'll fight a miniboss with a hammer. Once he's dead, climb up the small ladder at the back of the arena to find this item.
Once you have the teddy bear, talk to Jefferson. He'll jump on your back, which should immediately pop the achievement - although you should take him to the Flooded Fortress, since that's required for the True Ending and 100% achievements anyways.