You may cast Misthollow Griffin from exile.
5/1/2012 Misthollow Griffin can also be cast from a player’s hand.
5/1/2012 Misthollow Griffin doesn’t have an ability that exiles itself. Some other effect will be needed to get the card into exile.
5/1/2012 You must still pay Misthollow Griffin’s mana cost when you cast it from exile.
5/1/2012 Misthollow Griffin’s ability doesn’t change when you can cast creature spells: when you have priority during your main phase when the stack is empty.