Liquimetal Dragon

Flying, Haste, Indestructible
Whenever Liquimetal Dragon enters the
battlefield, you may discard a card. If you do, it
deals X damage to each other creature and player
equal to its power. Then exile Liquimetal
Dragon before combat.
Liquimetal Dragon's power is equal to the total
number of instant and sorcery cards you own in
exile and in your graveyard.