I was in a battle in ranked and they led with a grimmsnarl, and I led with a meowstic. Both Pokemon had prankster, so I went first with yawn. It told me it didn't affect grimmsnarl and I have no idea why. To clarify no other moves had been used at the time.
Moves that are "accelerated" by Prankster will automatically fail when used on a Dark type Pokemon, such as Grimmstarl.