Sure! Here's an example of a simple platformer battle game implemented as a single HTML file using JavaScript:
In this game, the player is represented by a yellow square (`#player`), and the enemy is represented by a red square (`#enemy`). The player can jump using the up arrow key, move left and right using the left and right arrow keys, and punch the enemy using the space bar. The player punches by briefly turning blue, and if the punch connects with the enemy within a certain range, an alert is shown indicating that the enemy is defeated.
Please note that this is a very basic example and can be expanded upon to add more features and functionalities.