Here is a concept kit I made in Scratch to teach the use of conditionals with a loop and operator. Here is a link to the puzzle, and here is a link to the solution.
Starfish, naturally, would like to fly his hot air balloon. As the programmer, your job is to create scripts that
1. Make gravity slowly pull the balloon down until it hits the ground. Since Starfish is in a balloon, we can forget acceleration.
2. Make the balloon go up if Starfish turns on the gas (spacebar), and then fall again if he lets go.
3. Show the Starfish's response to the action.
This project went through a number of iterations. I had some versions with all kinds of variables to calculate acceleration and create states for the Starfish, but I kept seeing if I could make things simpler.