Nintendo have announced a promotion that will let you register Nintendo 3DS or 3DS XL with Club Nintendo and one additional game (out of 15 selected ones) for a free copy of Super Mario 3D Land. Here's legalities:
"To participate in this promotion, Nintendo 3DS or Nintendo 3DS XL owners need to register their console and just one of 15 selected games with Club Nintendo between 27th November 2013 (15:01 GMT) and 13th January 2014 (22:59 GMT) to be eligible to request a free download code for SUPER MARIO 3D LAND by 13th February 2014 (22:59 GMT). Participants can then redeem their code and download the game from Nintendo eShop to any Nintendo 3DS, Nintendo 3DS XL or Nintendo 2DS system before 13th March 2014 (22:59 GMT)."
The following 15 games are included in the promotion:
Mario & Luigi: Dream Team Bros.
Animal Crossing: New Leaf
The Legend of Zelda: A Link Between Worlds
Donkey Kong Country Returns 3D
Fire Emblem: Awakening
Luigi's Mansion 2
Lego City Undercover: The Chase Begins
Sonic Lost World (Nintendo 3DS version)
Monster Hunter 3 Ultimate (Nintendo 3DS version)
Bravely Default (including Bravely Default: Deluxe Collector's Edition)
New Super Mario Bros. 2
Mario Kart 7
Professor Layton and the Azran Legacy
Enough incentive to pick up a 3DS for Christmas?