Yoonstone

When you cast a spell, you may add {2} to its casting cost and exile it without it having any effect. Place a Yoonstone counter on it. You may only have three spells exiled that way at the same time.
You may play spells with a Yoonstone counter on them from Exile as if you played them from your hand and as if they had Flash, without paying their Mana cost. Any other additional Mana costs these spells may imply are paid normally.