Technically, it's not "free," as you must spend $40 at clothing chain Old Navy. The retailer is also only giving out limited quantities of the game. Still, if your plans—or the plans of someone you know—include shopping here, it may pay for you to get there early.
Nintendo World News, citing the chain's Black Friday ad, says stores will have wristbands when they open on the Friday after Thanksgiving, and will give them out on a first-come basis. These wristbands can be redeemed for the game after buying your stuff and showing a receipt.
The chain has done video game offers in the past and all have been vaporized inside of one hour, so don't expect to bop on in at noon and pick up a free game.
Old Navy Giving Away New Super Mario Bros. U on Black Friday [Nintendo World News]