Well we've got a challenge for everything else...
Champion Challenge: Leaving the goal object permanently in the goal.
Clean Challenge: Leaving the board empty of all construction meterials.
Clean Champion Challenge: Self-explanatory.
Green/Brown Challenge: Using no powered objects.
Wheel-free Challenge: Using only sticks/rods.
Boomerang Challenge: Bringing the goal object back into the construction zone after hitting the goal.
Clean Boomerang: I made this up, but we can all figure out what the outcome should be.
How about UNHOOKED, completing all original 20 (soon to be 21) levels without connecting any rods or wheels to the goal object...?
Conversely, how about a STRAPPED challenge, completing all original levels where the goal object must be connected to a rod or wheel?