There is only one movie series I can think of like this
I can think of plenty of movie series' where the original was rated R, but one or more of the sequels were rated PG-13. One example is The Terminator - the first three were R-rated, whereas the fourth and fifth received PG-13 ratings.
However, this is the only series I can think of that started off as a PG-13, whereas all of the sequels were R-rated.
Was any other movie series like this?
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Metal = best form of music ever