As a language model AI, I can provide you with an example of a game where you can guess a number between 1 and 999999999999. However, please note that implementing a fully functional game within the constraints of a single HTML file and encasing it in script tags might not be possible. It's recommended to use external CSS and JavaScript files for better organization and maintainability.
That being said, here's a simple example of a number guessing game implemented in a single HTML file using JavaScript:
Guess the Number Game
In this game, users are prompted to input a number between 1 and 999999999999 using an input field. After clicking the "Guess" button, the script checks if the guess is correct or provides a hint if the guess is too high or too low. The game ends if the correct number is guessed.