You won't be creating Mario levels in the first half of 2015 anymore, though you should still be playing as Yarn Yoshi then.
Mario Maker, the Wii U game where you can make your own side-scrolling Mario stages, won't be coming out in the first half of 2015 anymore.
In October, Nintendo listed Mario Maker as being released in the first half of 2015. As of Nintendo's latest financial results briefing, Mario Maker is just slated as a 2015 release, implying it won't be out until the second half of the year.
Still listed for the first half of 2015 are Yoshi's Woolly World and Project Giant Robot, which join Kirby and the Rainbow Curse, Mario Party 10, and Splatoon as the Nintendo-published Wii U releases in early 2015.