I've always wanted to do a fleet like this one, as I think it'd be a way to add an interesting strength to the otherwise meh Cursed faction, especially in a larger game.
Here's how the fleet works: the Mist Walker and Sea Hag are the primary fighting forces, with the ability to hop out of a fog bank to intercept enemy gold runners or attack vessels. The smokepot specialist aboard the Sea Hag can also act to increase the gold runners' (Howl and Hangman's Joke) mobility by dropping fog banks near islands with gold on them. It'd even start the game by putting down a fog bank as near to the home island as possible, just to keep the gold runners moving.
The Mist Walker isn't the greatest sea monster of all time, but it is exceedingly quick, and would be perfect for chasing down the quickest of gold runners, as its lack of repair capabilities makes its usefulness as a frontline combatant questionable against dedicated warships, as a couple bad die rolls could make you miss out on your most expensive unit.
The main weakness is this fleet's inability to seriously combat a large threat positioned at its home island. Nothing could really stand up to something like HMS Grand Temple squatting at the home island, waiting for prey to dance out of the fog bank and straight to the bottom.
The UT, Lost, will vary from either a mild inconvenience if found by an opponent, to a serious boon if the player in control of this fleet finds it. It would allow for up to six new fog banks (or other terrain) to appear where you'd like them. It could involve dropping some reefs or sargasso seas under pesky enemies, or merely increasing your own fog hopping capabilities.