This version of the forehand loop is called a curve or hook loop. The ping pong ball veers sharply to the left away from the opponent. He has to chase it and deal with an uncomfortable spin, which tends to make the ball slip of his racket unless he drives it forward strongly. As a variation in a counterloop rally, it can open up the ping pong table for a put away shot.
The stroke is the same as in the loop off topspin, but you contact the ball a bit more to the right of center and wrap the table tennis paddle around the outside of the ball, pulling the follow through strongly to the left. Use a lot of wrist motion.
When your loop occurs, it's very important to stay down and you wait until the last moment to change direction. That means you make the basic shot like you bend your knees, you go forward, and the last moment you change the angle of your wrist.