Fog Wolf

Hidden {1}{g} (Rather than cast this card from your
hand, you may pay {1}{g} and exile it. At the beginning
of your upkeep, add a hidden counter. As long as a
hidden counter is on this, it can be played from exile.)
Flash
When Fog Wolf enters the battlefield, if it was
cast from exile, prevent all combat damage that
would be dealt by creatures your opponents
control this turn.