Great exercises for your obliques on the ball would be some stuff on the floor. So you can lie back, keeping your lower back pushed against the BOSU Ball so there's no space in between the BOSU and your back. And you're going to take it up and over to one side. And then you come back to the middle, down. So you lift, take it to one side, middle, down.
Another one would be to twist the opposite way. So you take the opposite elbow and you bring it towards your knee. Twist, up. Keep the elbow open, but you're just twisting. Your shoulders are automatically staying off the mat or the floor because you're on a BOSU Ball. To make it more advanced you can twist using one leg out, bring your knee in. And then even more advanced, you can twist by reaching for the leg.
Other exercises for your obliques is to hold a plank on the ball and then twist your hips from side to side keeping your legs as close together as possible. You're just going to twist and dip. And you'll definitely start to feel that in your oblique muscles.
You can also flip the ball over. And these are a little bit more advanced but will definitely get your obliques. You're going to hold on to the ball either by placing your hands in the middle, even distance apart, or you can hold on to the sides. And you're going to bring one knee towards your elbow, the opposite one. So you twist, and then you come back. And then you twist, and you come back. And you want to try and get as far as you can towards your elbow. If you just get a little bit of distance even right there, that's good enough. You can just work on it.
And then, another one for your obliques is to go on the outside. So again, you bring you knee towards your elbow, keeping your back flat, keeping your neck in line with your back, keeping your hips up, not dipped. And you just bring that knee towards you elbow, as close as you can get it.