Zaolya, Prowler of the Night

Other wolf, werewolf and vampire creatures you control have +2/+2 and first strike.
If a creature you control would transform this
turn, you may pay {b}, Sacrifice two creatures. If
you do, negate target triggered ability from
another creature until the next main phase.
At the beginning of each upkeep, if a player casts
four or more spells last turn, transform Zaolya, Prowler of the Night.