Sure, here's an example of a simple 3D horror game implemented as a single HTML file using JavaScript:
This is a basic game where you play as a player represented by a red square. The objective is to avoid the green monster squares (pictogram equivalent) that move around the canvas. If the player collides with a monster, an alert message will pop up indicating game over. You can control the player's movement using the arrow keys on your smartphone.
Please note that this is just a simple example to demonstrate the concept of a 3D horror game, and it can be extended and modified to suit your specific requirements and visual style.