I'll be streaming user-submitted levels again at about 10PM Eastern (one hour from now). Post a code for a level and I'll stream it. One code per GAFfer. It can be for your stage or someone else's stage of your choice. Just quote this post with the code so that I can easily see it. First come, first served.
In the meantime, you could also give my second stage a try:
Goomba's Spelunking Boots
F13E-0000-004C-86C9
Youtube playthrough (secret areas are spoiled)
For this one, I made an attempt at creating a somewhat "genuine" SMB3 stage, with easy to moderate difficulty and based around a single game attribute (Goomba's Shoe). It's fairly larger than your standard SMB3 course, but I think it mostly meets the goal.
I originally wanted to make the underground area roughly twice as large, with more challenge rooms and secrets to uncover. However, I hit the block limit and had to cut things short. I could have added more areas by hollowing out the walls and using single-tile borders for all the rooms, but I felt that that would have ruined the aesthetic.
Previous stages:
Board the Airship
Thanks for the comments left on the first stage. I don't think I'll meticulously revise and reupload any stages unless they're outright broken, but every bit of advice helps for future efforts.