Mercy is Weakness

When: Your Shooting or Fight phase.
Target: One Adeptus Astartes unit from your
army that has not been selected to shoot or fight
this phase.
Effect: Until the end of the phase, each time a
model in your unit makes an attack that targets
a unit that is below Starting Strength, that
attack has [SUSTAINED HITS 1],
and when making such an attack, if the attacking
model is a Vehicle, a successful unmodified Hit
roll of 5+ scores a Critical hit.