Parthan Aristocrat

When Parthan Aristocrat enters the battlefield, if its stalk cost was paid, you
draw a card and lose 1 life.
Stalk {2}{b} (At the end of each block step, if
there is an unblocked creature attacking you, you
may cast this card for its stalk cost. If you do, choose an unblocked creature attacking you. This creature blocks that creature.)