This update holds the keys to the castle.
Keys with locked doors, skewers from Super Mario World, and Super Expert difficulty will release on March 9 in Super Mario Maker, shown off during today's Direct.
Keys can be hidden in the stage or in an enemy, creating mandatory boss battles, or be locked behind a handful of pink "key coins."
Super Hard difficulty will unlock new costumes. Tetra from Windwaker was shown.
Super Mario Maker's Bookmark site will also add new rankings and features.