These moderate exercises for the Swiss ball (aka therapy ball, stability ball, exercise ball, etc.) will help increase your core strength and stability. If you aren’t quite ready for this level, check out my basic Swiss ball exercises.
The first two moderate Swiss ball exercises are crunches on the ball. You can do them straight up and down, or you can cross over to get your oblique core muscles.
The next two exercises for the Swiss ball are a tabletop bridge, and a bridge with your feet on the ball. Both of these are hard, but in different ways. Make sure you are able to stabilize the ball so you don’t fall off. These are great for the hamstrings, and glutes, as well as the core.
Then you have the modified plank and modified side plank. Try to keep your butt tucked in by squeezing your glute muscles in, and try to keep your body in a straight line.
Finally you will do a dead bug with the Swiss ball in between your arm and leg. You can do opposite arm and leg, or same side. Try to keep a pelvic tilt when doing these.