Arrow keys to move. The only difference between a normal platformer and this is that here everything is upside-down. So down arrow key to jump.
I was playing around on scratch when I started playing a project by @JBGT, called Inverted: A Platformer v 1.0.0. It is a game where you are a yellow block and the controls are switched. The right arrow key moves you left, The left arrow key moves you right, the screen is upside-down, and up arrow key makes you jump-DOWN. Here is the link: https://scratch.mit.edu/projects/60238664/ P.S. All the scripts are mine. Inspiration goes to @JBGT. Sideways: https://scratch.mit.edu/projects/96930100/
