The past few years have seen video game platforms use advent calender-style promotions to keep people returning to their site to buy new games. The Epic Games Store free mystery games, which pop up a couple of times per year, are perhaps the best example of this, but now a traditional retailer has gotten in on the action. Tech retailer Best Buy is hosting a mystery game promotion where it is selling 10 games at a huge discount, with one new game available to purchase each day.