Sure! Here's an example of a simple 2D endless zombie shooter game with a wall-building skill. The game will be implemented as a single HTML file with JavaScript enclosed in script tags. Please note that this is a basic example to give you an idea, and you can modify and expand it as per your requirements.
To play the game, open the HTML file in a web browser (preferably on a smartphone) and use the arrow keys to move the player. Press the spacebar to activate the wall-building skill and create temporary walls to trap zombies. Avoid getting caught by any zombies. When a zombie collides with a wall, both are eliminated. The game ends if a zombie collides with the player.
Feel free to enhance the game by adding features like a scoring system, different levels, better graphics, sound effects, and more gameplay elements.