Sure! Here's an example of a simple Pokémon-themed game implemented as a single HTML file using JavaScript:
In this game, you control a red square (representing the player) using the arrow keys on your smartphone. The objective is to catch the green square (the Pokémon) by moving the player over it. Once caught, an alert message will be shown indicating that you successfully caught the Pokémon.
Please note that this is a simplified example and can be further enhanced with additional gameplay elements, graphics, and features.