Create a zombie shooter game by creating gun, ammo and zombie sprites. Keep the scratch cat and make the gun go in it's hand. Make the ammo go on the tip of the gun and use clones to make it shoot. You can use clones on the zombie too.

Make it that when the zombie touches the cat, it is game over.
And when the bullet from the gun touches the zombie, the zombie gets killed. Give the game a theme by getting a backdrop (e.g a galaxy backdrop for a space theme).