There is a red enemy which you have to kill with the help of your mouse pointer. How? You have to click on the enemy to kill it and after that there is a satisfying small blood splash . But if you miss the target it would duplicate itself and that would be a big problem for you and when it touches the green player which would be you in the game it will decrease your game health by 1. you can  also move in the world but don't go where you can't see!