Teferi, Archmage Returned

Flash
When Teferi, Archmage Returned enters the battlefield exile target spell.
{w}{w}{u}{u}, exile a card from your hand, {t}:
You may cast any spell exiled with Teferi,
Archmage Returned without paying its mana cost.
In my youth I learned how dangerous time could be.
Now it's your turn!