Apparently people find my level (ID removed because I deleted the level) a bit too hard, so I decided to give some tips that make it easier (besides getting the Propeller Mushroom):

You can grab that spring in mid-air.

Stand here when you're placing it.

Use that question block to release a Koopa...

...you can kill the enemies downstairs with it.

Use the Question Switch and throw the shell of a Buzzy Beetle downstairs. Repeat if the way to the exit isn't cleared and Bowser is still alive. I found out that Bowser can die without clearing the exit like here: http://abload.de/img/wiiu_screenshot_tv_01cwz5z.jpg That's unintended and I have to edit that. It's getting really hard when that happens, I'd throw the Question Switch on the Conveyor that it falls down go to the room downstairs as Super Mario and hope for the best. But yeah, that's unintended and unfortunate.

Throw another shell to kill enemies and use one to protect your front when you're Small Mario. But my advice is to take another mushroom from the pipe near Bowser when you're small.

Just made another level, this time it emphasizes having fun with the level. It's really easy to beat, but there's a surprise hidden (not really all that hidden) in the level.
Code: 2864 - 0000 - 0037 - 105E
I know I've been posting a lot, I just want to share all the levels I've been making.

edit: 

edit 2: 

Updated my auto-level.

I think tonight I'll do a rundown of the levels posted here. In general, I found the levels posted by our users to be better than the random ones listed by Nintendo.

My second level:

 

Once upon a starry night (D3E7-0000-0035-D591) Is also simple but harder

I picked this game up at the Nintendo World Store on launch day, but haven't got home to play it yet. Can't wait!

Yeah this is where Super Mario Maker excels compared to say LittleBigPlanet. In SMM I've already made 3 levels in 3 days, whereas in LBP it's more like 3 levels in 3 months.

And yeah I'll play your level along with everyone else's new ones in a bit!

Totally agree! Making a level doesn't feel like a chore, the ease of use of the editor is nothing short of brillant. You can play test a section, adjust what's wrong with it, play it again, rinse and repeat until you're happy with the result and it's so seemless.

The random listing by Nintendo has been a terrible area to pull levels from.  I find that their 100 Mario Challenge selections aren't AS bad, but still nothing close to the quality I am seeing in this thread.

I've spent way more time making levels than playing them.  I'll probably get around to more of the levels here a little later.  Don't really know if people actually enjoy my levels when my most starred level is the joke one.

I have only gone through one or two here myself, but they were well put together.  I try to star every level I use a code for though, that way those folks can upload more levels once they hit the stars necessary.