Sure! Here's an example of a simple multiplayer shooting game implemented as a single HTML file with JavaScript:
In this game, you control a blue square representing the player using the left and right arrow keys on your smartphone. Your goal is to shoot the red squares (enemies) by tapping/clicking on the canvas to release a yellow bullet. If the bullet hits an enemy, it will be reset to a random position at the top of the canvas.
Please note that this is just a basic example to demonstrate the concept of a multiplayer shooting game. You can enhance and modify the game mechanics, graphics, and features based on your requirements.