This Super Mario Brothers Flash online game is 4.90 MB in size, so please allow plenty of time for it to load...
This is a huge game with multiple levels to explore. Consequently, the game is slow to load all the data for each level, but if you are patient you will hopefully find it worth the waiting. The controls for moving Mario are as follows: Cursor Left and Right keys (Arrow keys) = Walk around; Up Arrow = Jump; Down Arrow = Walk through doors / jump into paintings; Space Bar = Use Fludd. Other controls are: Page Up and Page Down = Toggle Quality; Home = Return to Castle / Title Screen.
Your progress will be saved automatically so that you can continue at the same level you were playing previously when you return to the game in the future, but you must play it in this website again in order to be able to re-use the saved data. (You can delete the save file via the Extras option on the game start screen if you later wish to reset the game.)
If the game runs slowly on your machine, try reducing the graphics quality by clicking on the control in the top right of the game window, or by pressing Page Up/Down. If you experience any problems with the game, such as jerky movement of Mario / difficulty landing on platforms, set Auto Quality to "Off" on the game start screen prior to playing it again, and then select "Low" graphics quality.
Here is a Super Mario Brothers desktop wallpaper picture (800 x 600 pixels):
To use this picture as your desktop wallpaper, right-click on it with your mouse and then select "Set as Windows Wallpaper" or "Set as Background", or whatever similar option your particular browser provides in the right-click pop-up menu.