You can find below the prompts I used or imposed to myself to make the levels, which are presented in the order of creation.
You can probably try to guess the prompt for each level after playing it. :)


SO MINT AND FRESH
-Create a 9th level for the Special World in SMW. (submitted for a BotB SMW battle)


SPRINKLER CLOUDS
-Create a level using only these randomly generated sprites: keyhole, growing vine, horizontal fish, line-guided rope, floating orange platform and bullet shooter. (prompt taken from a BotB SMW battle)


ECHOES OF ANGLES
-Create a level built mainly from slopes.


COUNTERFEIT MONEY
-Create a level using these randomly selected index of graphics: 7 (Normal 2) for FG/BG GFX and 8 (Banzai Bill) for sprite GFX.


MATTER FOR MODELING
-Create a level built mainly from throw blocks.


SMALL SWITCH PALACE
-Create a switch palace level in only 10 minutes.


CASTING PLAINS
-Create a level based one of the screens appearing on the enemy roll.


SUITE ROYALE HUIT
-Create a level reminiscent of maze fortresses from SMB3 (e.g. 3-Fortress 1 or 8-Fortress).


PRECEDING THE EVENT
-Create a level based on one randomly selected level from SMB2J (world C-2).


TUBULAR FOR DUMMIES
-Create a level keeping all the sprites' placement from TUBULAR.