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.
