The Nasty level in crayon physics has two stars to collect. Although its possible to collect both stars in a single go, this method shows collecting each of the stars in separate goes.
To collect the first star, first block the ball at the top. and create structures as in image below.
Delete the blocking box to collect the first start. The ball falls down and comes for second go. Block the ball and build the next set of structures as in below image.
Draw both structures together along with guarding wall at the left bottom corner to collect both stars in a single go.