Koráki, the Spell Thief

At the beginning of your end step, reveal the top
card of your library. If it's an instant or sorcery
card, you may draw a card, then create a 1/1 blue
Human Spellshaper creature token with "When
this creature enters the battlefield, you may exile
an instant or sorcery card from your hand" and
"{x}, {t}, Discard a card: Copy the exiled card.
You may cast the copy without paying its mana
cost. X is the mana value of the exiled card."
"Time, as it grows old, teaches all things."