public void execute() {
            // get all creatures
            CardList cards = AllZoneUtil.getCardsInPlay("Umbra Stalker");
            for (Card c : cards) {
                Player player = c.getController();
                CardList grave = AllZoneUtil.getPlayerGraveyard(player);
                int pt = CardFactoryUtil.getNumberOfManaSymbolsByColor("B", grave);
                c.setBaseAttack(pt);
                c.setBaseDefense(pt);
            }
        }