I like Jumping Rope. It look me some time before I figured out how to play the second level.
The first level the girl jumps when you press letter Z, the second level the girl continues to jump when you press letter Z but the boy (at least I think it's a boy) jumps when you press letter X, and on level three the third girl jumps on letter C. I haven't reached level four yet, so I don't know what happens then. I'm guessing...letter V?
This should be described in the Instructions
