This update holds the keys to the castle.
http://www.nintendoworldreport.com/news/42070/new-mario-maker-course-elements-coming
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.
I have never beaten the Expert 100 Mario mode ever due to troll levels so if they move in into their own weird category that will be great.They already did this a while back to keep those levels out of Expert. Super Expert just wasn't a mode you could play before this upcoming update, but it was a category you could see on the bookmark website and those levels already don't appear in Expert mode.