Sure, here's a simple 2D battle game implemented as a single HTML file, including JavaScript. It uses pictograms for the game elements and is designed for smartphone operation. You can play it by running the HTML file in a web browser:
2D Battle Game
You can save the above code as a ".html" file and open it in your web browser. The game presents you with a player and enemy, represented by pictograms. You can attack, defend, or heal using the buttons provided. The health of each character is displayed below their pictogram. The game will end once either the player or enemy reaches 0 health. Enjoy the game!