This is actually a pretty cool update so I'll post everything here:
"Super Mario Maker will receive an update on March 9, Nintendo announced during its latest Nintendo Direct.
The update will come with a new "super expert" mode for its 100 Mario Challenge, which will unlock new Mystery Mushroom costumes. This unlocks after clearing expert mode and adds 6 more levels. Clearing these unlocks the new costumes.
It will also bring additional options for the level designer. These include Thwomp skewers from Super Mario World and mandatory boss battles, thanks to the addition of keys.
Nintendo also shared that more than 6.2 million courses have been uploaded since launch."
Also, pinks coins are going to be added. When you collect 5 a key will appear, so you can make levels that require finding all the coins in order to get they key to a door.
I have to say I'm excited for the keys because I like having mandatory boss battles in my levels 
