Sure, here's a simple implementation of a Mario game using JavaScript, enclosed in script tags within a single HTML file:
This implementation creates a simple game where the player (represented by a red box) moves from left to right on a game board. The goal is to avoid colliding with a block (represented by a green box) on the right side of the board. If the player collides with the block, a "Game Over!" message is displayed and the player and block positions are reset. The player moves every 200 milliseconds.