Okay, Goomba Lair: F7F9-0000-0069-35B0. It's my first course, uses nothing but the intial set of items, and any feedback would be nice (provided it isn't Joseph2302 saying "it sucks" and nothing else)
It's certainly pretty darn good for a level that only uses the initial set of items.
Originally I was going to wait the full 9 days for everything to unlock, but I wasn't interested in creating a level without invisible blocks (day 6) or sub-areas (day 9) that I could use for secret bonus items and areas.
To unlock everything faster, first make sure you've used all the parts you have available at least once (none of them should have a red exclamation mark by them). After about 5 minutes of doing stuff in the editor, the game will pop up a dialog and tell you that a new shipment of stuff is on the way. When this happens, fill your entire course with blocks, preferably using the copy/paste tool (L to select an area of blocks; ZL to copy them). Eventually the game will tell you that your stuff came earlier than expected.
Repeat the instructions of the previous paragraph until you've unlocked everything (the game will tell you when this has happened).