Sure! Here's an example of a simple 3D slow zombie shooter game implemented as a single HTML file using JavaScript. Please keep in mind that this is a basic implementation and can be further expanded and improved.
This implementation creates a simple game canvas where the player controls a blue square using the arrow keys on a smartphone. The player needs to avoid the green square that represents the zombie. If the player collides with the zombie, it's game over.
Note that this is a basic example, and you can enhance it further by adding more features such as scoring, multiple zombies, additional levels, sound effects, etc., according to your requirements and programming abilities.