Get in the half-sit-up position with your feet anchored. Maintaining this half sit-up position while doing any movement with the arms will challenge the abs, and this one hits the delts as well.
Try to keep your spine and neck as neutral as possible. Go light and do the exercise for one continuous minute, or go a bit heavier and aim for 10-15 reps.
Single-leg trap bar exercises in the style of the Reeves deadlift (hands on plates, not bar) provides the perfect stimulus for crushing every muscle in the body.