Play the original Super Mario Bros online for free.

How to play Super Mario s

Use arrows [↑→↓←] or W-A-S-D keys to move Mario, to jump higher hold the button.
Use Shift/CTRL to Fire/Sprint. Use P to pause and M to mute.

You can switch the levels yourself.
The game has a fun function. This is map generation. Change it on click and rejoice!