Sure, I can help you create a simple creature platformer game in a single HTML file using JavaScript. Here's an example implementation:
This implementation sets up a blue box (representing the player) that can be moved using the arrow keys on a keyboard. The player can move left, right, up, or down by 10 pixels each time an arrow key is pressed. The position of the player is updated and rendered on the screen accordingly.
Note that this is a basic framework for a platformer game, and you can enhance it further by adding sprites, obstacles, levels, and more game mechanics as desired.