I've made no secret of the fact that I really rather like NSMBU, even though it's built on top of the existing Mario universe in ways that aren't necessarily all that innovative; just polished. It appears, though, that it's not just built on existing Mario games — it could well be one.
Digital Foundry has done another of its rather exhaustive deconstructions of the NSMBU engine, and the art assets within it, matching up New Super Mario Bros U running via HDMI with New Super Mario Bros Wii running at 1080p on the Dolphin emulator.
The results? There's a lot of re-used assets, and not quite as much HD as you might have hoped for. It's an interesting read, given that Nintendo appear to have mixed between upscaled existing assets and brand new ones:
Other improvements include higher resolution alpha for dust clouds, which appear at Mario's feet wherever he runs as opposed to just during sliding and landing animations on Wii. The sharp-eyed will also spot the spark effects after bopping Goombas bring out a bright bloom effect, which only appears as a simple sparkle animation in the preceding game. The detail bump on the static gold coins is also a huge step forward, with the blocky 2D sprites seen on the Wii version being eschewed in favour of the fully polygonal, spinning kind on Wii U.