Sure! Here's an example of a simple 2D zombie shooter game implemented as a single HTML file using JavaScript:
In the above game, the player (represented by a green square) can be controlled by moving the mouse within the game canvas. Zombies (represented by red squares) are randomly generated every second and move around the canvas. The game detects collisions between the player and zombies, and if a collision occurs, a game over message is displayed.
Please note that this is a basic example. You can modify and enhance the game by adding more features, levels, graphics, sound effects, etc., based on your preferences and requirements.