Sure, here's an example of a simple 3D slow zombie shooter game implemented as a single HTML file using JavaScript:
This simple game sets up a canvas and allows the player (represented as a blue square) to move using the arrow keys on their smartphone. The goal is to avoid the green zombies (represented as circles) that move slowly towards the player. If the player comes into contact with a zombie, the game over logic (currently just a console log) is triggered.
Please note that this is just a basic implementation of a game and can be expanded upon with additional features, graphics, sound effects, etc.