Sure! Here's a sample implementation of the game you described. You can copy and save it as an HTML file to play:
In this game, you can control a blue player using the arrow keys or 'w', 'a', 's', 'd' keys to move it around. The goal is to kill zombies by pressing the 'l' key. Every 20 zombies killed, a special green zombie has a one-in-a-million chance of appearing, which can also be killed by pressing 'l'.
The number of zombies killed is displayed on the top left corner of the canvas. The game runs continuously until you close the HTML page.
Note: The implementation above is just a simplified example based on the information provided. You can modify and enhance it further according to your specific requirements.