Sure! Here's an example of a platformer game using JavaScript and HTML:
In this game, the player controls a blue character using the arrow keys. The character can move left and right within the game container. There is also a red boss that moves from right to left continuously. If the character collides with the boss, a game over message is displayed.
Note: This is a simplified example and only includes one level with a single boss. You can extend the game by adding more levels and bosses as per your requirement.