Bring down the Beast

Use this Stratagem in your Shooting phase, after
shooting with a GREY KNIGHTS unit from
your army. Select one enemy VEHICLE or
MONSTER unit that was chosen as a target for
that unit's attacks. Until the end of that phase,
when resolving an attack made by a model in a
friendly GREY KNIGHTS unit against that
enemy unit, you can re-roll the wound roll.
Together the Grey Knights can bring down any foe.