press the green flag and he will chase the mouse cursor when you click press space to toggle the reference image :) update 8/4/2021: I found my old svg and imported it as costume 3. Scratch didn't read all the advanced gradients I applied with Inkscape correctly but did a better job than I expected!
old: I used Inkscape to make the sprite with vectors but all the layered gradients crashed Scratch on import so I separated all 6 sprite parts, imported them as a .png and reconstructed Bowser Jr. There are 2 costumes provided, Bowser Jr constructed and with individual parts for posing your own different costumes. song is From the Pinnacle to the Pit by Ghost