Memory Stone

Imprint —When Memory Stone enters the battlefield, you may exile an instant card from
your hand with converted mana cost X or less.
{x},{t}: You may copy the exiled card. If you do,
you may cast the copy without paying its mana
cost. X is the mana value of the exiled card.
{t}: Exile Memory Stone. If you haven't cast a
spell named Memory Stone this turn, you may
cast it from exile this turn.