Brianna, the Liberator

When Brianna, the Liberator enters the
battlefield or attacks, each opponent discards a
card.
Brianna, the Liberator has +3/+3 as long as
its attacking a player that has no cards in hand.
Revive —{b}{r}, Pay 3 life, Exile one other card
from your graveyard. (You may cast this card from
your graveyard by paying its revive cost.)