Use the arrow keys to move. Jump on as many goombas as you can before you die. You can go down one tube to appear in the other. The goombas might glitch at first and come out of the ground. I can't figure out why. They will just start appearing on the ground after one or two goombas appear. Mario might do that too. Other than that I think it's pretty cool.
I got my platforming info from How to make a platforming game by Chronicle. Thank you for your help! I might decide to add a new underground stage. To get to it you will go down the tube in the middle.