Judging by some of the reviews for the DLC, some people appear to be confused by the installation process. Hopefully this guide will clear it up.
Who is the Musketeer?
The Musketeer is a reskin of the “Arbalest” hero. She is virtually identical to her; the only differences being how she looks, the icons for her skills and the appearances of her trinkets. They all function the same and give the same bonuses (with the exception of the “Color of Madness” DLC’s personal trinket, which has different stats from the Arbalest’s). She also has entirely different lines for critical hits and lines relating to afflictions/virtue.
She used to be exclusive to backers of the kickstarter that had pledged a certain amount of money but was made available to everyone last june.
How to add the Musketeer to the game
Just go to the DLC’s store page and click on the download button. For some odd reason, instead of installing new content like you’d expect it to do, it will attempt to boot the game. That’s normal; let it open Darkest Dungeon. Then close the game.
If you have none of the expansions you should see a new “Downloadable content” square that wasn’t there before on your Darkest Dungeon’s library page. Uncheck the Musketeer DLC and re-check it; your steam client should now download a small update for the game and the DLC should brighten up.
You should now be able to find and recruit the Musketeer in the stage coach.