Countess of Masks

When Countess of Masks enters the battlefield,
exile a creature card from your hand face-down.
When Countess of Masks dies, if it blocked this
turn, put a card exiled with it onto the battlefield.
Stalk {4}{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.)