Sure, here's an example of a single HTML file that implements an endless side-scrolling dungeon runner game with JavaScript:
This HTML file includes JavaScript code to create an endless side-scrolling dungeon runner game. The player character can jump by pressing the space bar and needs to avoid colliding with red obstacles while collecting yellow coins. The game will keep track of your score and display a game over message when a collision occurs. The high score is also stored and displayed. The game will restart automatically after game over.
Please note that this is a simplified implementation for demonstration purposes, and you can further enhance the game with additional features, graphics, sounds, and animations as per your requirements.