Shantu, Arcane Savant

When Shantu, Arcane Savant enters the battlefield, you may search your library for an
instant or sorcery card and exile it.
{x}, {t}: Copy the exiled card. You may cast the
copy without paying its mana cost. X is the
converted mana cost of the exiled card.
Whenever a player casts an instant or sorcery
spell, Shantu phases out.