As part of a 10 day challenge I made this example local coop game for my portfolio.
This needs debugging, very short dev window.
Shift seems to be ignored in the HTML version, depending on the browsers, but you can map a different input.

Inspired by mario games.
Pressing plus adds player characters to play with. Collect level coins for 100%. Life coin parts give a life on 100 collected. There is a shop for the money coins.