Man of Medan, the first episode in Supermassive Games' Dark Pictures Anthology, is really designed to be played with mates. Sure, you can play on your lonesome if you want, but the online co-op mode is where the B-movie romp really flexes its horror muscles. This mode normally requires both players to own the game, but for the next month that will no longer be the case.
It's a shame it missed Halloween, but you can keep the scares going for another month by inviting a friend to download a trial version of the game that lets them play a full playthrough of the Shared Story mode. Players only get a single pass to give out, and the pass will expire in a month if it's not been used.
While Man of Medan's multitude of choices and endings means that you'll probably want to play it more than once, a single playthrough will still keep you occupied for a couple of evenings and, even if you miss clues or make terrible mistakes that end in everyone dying, you'll still get a complete story.
Unlike the offline pass the controller mode, Movie Night, which assigns each player a specific character, online co-op makes you and your partner keep switching as the story dictates, so you'll get to play as everyone. While you'll spend a lot of time working with your co-op buddy, Man of Medan also revels in splitting up the party, messing with your head and fostering distrust, pushing you into familiar horror traps.
If you've got automatic updates turned on, you should see a second version of Man of Medan in your library. That's where you'll be able to invite your friend by sharing the product code, and it's also where you'll both play. After they've registered the code, you can start up the Shared Story mode and invite them normally through Steam. The second version should also be available to download manually if it's not already installed.
The Curator's Cut mode has also been added with the update, letting players who have completed at least one solo playthrough start a new game with alternative scenes and perspectives unique to the mode. This is only for owners of Man of Medan, however, and not available with the pass.