You reminded me of challenge puzzle from my game Fire Leaf Water. There's a 10th level challenge in which player could complete normally or complete the star challenge. The latter requires scoring at least 400 or 500 depending on number on the star block. I could complete the other 10th level challenges but that one level really puzzled me.
I almost wanted to reduce the score requirement or whatever but I didn't give up and managed to beat the challenge. Therefore I am sure the challenge is doable.
That made proud of being able to create challenging puzzle which really challenged me ;D.