Nintendo just recently confirmed that a new DLC stage is coming to both versions of Super Smash Bros 4 to celebrate Super Mario Bros's 30th Anniversary; This new stage is Super Mario Maker. From the footage below, it is shown that the stage is completely different each time that it's loaded and it builds, changes, and/or makes repairs onto the stage as the players battle. This is certainly an unexpected surprise as I don't think ANYONE was expecting this.

This stage will be released on September 30th and if past pricing is any indication, then it'll cost $1.99 USD for one version and $2.99 USD for a bundle containing both, but until then, I'll be seeing you.