Vradroz, Ruinous Drakon

Flying, trample
When Vradroz, Ruinous Drakon attacks, you
may choose an instant spell from your hand or
that you own in exile with mana value three or
less. You may cast that spell without paying its
cost. If you do, put a number of +1/+1 counters
equal to its mana value on Vradroz.