Twilight Trickster

Flying
When Twilight Trickster enters the battlefield, separate the top five cards of your opponent's library into two piles without looking at them. Your opponent chooses one of them. Put the chosen pile into your opponents hand and exile the other pile. You may and cast that card for as long as this creature is on the battlefield. You may spend mana as though it were mana of any type to cast that spell.