Entropic Strike If a model has this special rule, or is attacking with a Melee weapon that has this special rule, a To Wound roll of a 6 wounds automatically, regardless of the target's Toughness. Against vehicles and buildings, an Armour Penetration roll of 6 that does not cause a penetrating hit automatically causes a glancing hit.
Rending If a model has the Rending special rule, or is attacking with a Melee weapon that has the Rending special rule, there is a chance that his close combat attacks will strike a critical blow. For each To Wound roll of a 6, the target automatically suffers a Wound, regardless of its Toughness. These Wounds are resolved at AP2.
Similarly, if a model makes a shooting attack with a weapon that has the Rending special rule, a To Wound roll of 6 Wounds automatically, regardless of Toughness, and is resolved at AP2.
In either case, against vehicles, each armour penetration roll of 6 allows a further D3 to be rolled, with the result added to the total. These hits are not resolved at AP2, but are instead resolved using the model/weapon's AP value.