Sure, here's a simple game implementation using JavaScript and HTML that you can play as a finished game on a smartphone:
This implementation creates a game where you need to protect the octopus (represented by a octopus emoji) from the evil monster (represented by a monster emoji) on a smartphone screen. You can move the octopus around by touching and dragging it on the screen. If the octopus collides with the monster, a "Game Over!" message will appear, and the game will reset.