A rock type is always slower than a "lighter" type.
Is there an item in game which reverse the gravity ? (it seems to me that the little girl said this) the girl who leave with the friend of keteleria. But I am probably wrong.
There's a move called Trick Room, when you use it, slower pokemon move first.
There's also two items called Iron Ball and Lagging tail, they both make the holder move last, so you can Trick it into your opponent.