Mordred, Knight of Treachery

When this card enters the battlefield: destroy a creature you control. Then deal damage to both players equal to that card's converted mana cost.
Your opponent may choose to do the same.
When this card attacks, clash with an opponent.
If you win the clash, this creature is unblockable
until the end of the turn. If you lose the clash,
this creature gains double strike.
At the end of a turn this card attacked: you may
send the top card of each player's library to the
graveyard.