Sure, here's a simple game called "Kaiju Takedown! Mechs vs Kaiju" implemented as a single HTML file using JavaScript and enclosed in script tags:
This game is a simple "Kaiju Takedown!" where the player controls a mech represented by a blue rectangle. The objective is to avoid colliding with the red rectangle representing the kaiju. The mech's position can be controlled by swiping left and right on the smartphone screen. The game keeps track of the score (time survived) until the player collides with the kaiju, resulting in a game over screen displaying the final score.