A great bodyweight exercise that will work your core and hit those obliques are cross body mountain climbers. To do these you want to start off in a push up position making sure that your midsection isn’t going towards the floor and you also want to make sure that your butt isn’t up in the air either. You want your body to be in a nice, straight line.
Once you have correct form to start the exercise, you will bring your left knee towards your right elbow as your need and return back to the starting position. Then you will bring your right knee towards your left elbow and bring your leg back to the starting position.
Depending on your fitness level, you can do 3 sets of 10 reps of these, 4 sets of 12 reps, 3 sets of 15 or if you’re advanced, 4 sets of 25 reps.
Let me know how you do!