Updated: Blizzard PR representative Christine Yeo addressed Marin's availability in a statement:
"We haven't set a firm time on when it ends, but it will at least exist for now through the Hearthstone Kobolds & Catacombs expansion slated to release in December. Also those who got BlizzCon ticket or virtual ticket will get the golden version of Marin."
It wasn't the biggest announcement to come out of Blizzcon—that crown may well go to the official World of Warcraft vanilla servers, depending on who you ask—but Blizzard did give Hearthstone fans some delightful news: they're getting a free legendary card, and all they have to do is boot up the game. With the release of today's patch, they've made good on their promise: neutral legendary Marin the Fox is now available for use in-game.
Marin is a Soulbound card, meaning he can't be crafted or disenchanted, so it's lucky that you just have to log in to claim him. His effect, giving your opponent a 0/8 treasure chest which gives you a powerful card when it dies, has already prompted some interesting deck ideas. At the time of writing, streamer and pro player Savjz is tinkering with Marin in a funky Warlock deck.
It goes to show how much fun one free card can inject. Of course, with the Kobolds & Catacombs expansion due out this December, there many more new cards on the horizon, including unique legendary weapons for every class, the new 'recruit' ability, and a single-player dungeon-crawl mode. You can learn more about the expansion here, and read the full patch notes for today's update in this blog post.
At Blizzcon, Hearthstone director Ben Brode said logging in today, November 6, will get you Marin (Blizzcon attendees got a golden version). I've reached out to Blizzard to confirm how long Marin will be available as a freebie and will update this story if I receive a reply. In any case, play it safe and log in by day's end.