Sure! Here's a sample implementation of the game you described using HTML and JavaScript:
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This HTML file includes the necessary CSS styles and JavaScript code to create a game where you can kill bad guys to collect money. The game area is represented by a div with the id "gameArea", and the bad guys are represented by bomb emojis. To kill a bad guy, simply click on it or click on the skull emoji to earn money.
Every 10 seconds, a new bad guy will spawn randomly in the game area. Every 30 seconds, an upgrade screen will appear, allowing you to upgrade your skills to earn more money in the future.
Note: It's important to remember that this is just a simple example for demonstration purposes. In a real game, you would want to consider things like game balance, graphics, sound effects, and more.