In today's Nintendo Direct, it was revealed that the Wii U title Sonic: Lost World would receive a free Yoshi's Island themed level.  The Yoshi's Island Zone DLC level is available as a free download on the eShop right now.  It's worth noting that the DLC can be purchased on your account even if you don't currently own the game it is tied to.

Source: Nintendo Direct (12-18-2013)