Any skill that begins inverted (top person is upside, or technically, head is below her shoulders and at least one leg) and transitions to an upright position would be an inverted transition to prep level.
I assume you are referring to the list of Advanced skills that will put a Level 4 team in the highest range. Here are some examples:
An all girl braced rewind stunt that gets caught in a load in position is NOT advanced.
The stunt that Stingrays Small Senior L5 performed at Worlds, where some of the stunts flipped up to an extended position and some flipped to prep level. The ones that flipped to prep level would satisfy this criteria. The ones that flipped to extended level satisfy the Elite criteria.