Lethal Infiltrator

When Lethal Infiltrator enters the battlefield, if its stalk cost was paid, put two
-1/-1 counters on the creature it's blocking.
Stalk {4} (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.)