Next week, a DLC for New Super Mario Bros. U comes out! You play as Luigi and play up to 4 players! One player can play as Nabbit on Multiplayer modes. Nabbit can pick up power-ups which result to 1ups at the end while not getting hurt by enemies! There are 80 levels and almost all the levels start with 100 seconds, so there are VERY short levels. The DLC comes out on June 20 in all regions, while the US release for the Standalone version comes out on August 25.
Other Differences include Luigi's higher jump, and probably world maps. That is all!