Blade Of Perdition

A model attacking with this weapon never receives +1 Attack for fighting with two Melee weapons (see page 177).

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 their close combat attacks will strike a critical blow. For each To Wound roll equal to or higher than the value listed, the target automatically suffers a Wound, regardless of its Toughness. The controlling player may choose to resolve these Wounds at AP 2 instead of the weapon’s normal AP value.
Similarly, if a model makes a Shooting Attack with a weapon that has the Rending special rule, a To Wound roll of equal to or greater than the listed value wounds automatically, regardless of Toughness, and is resolved at AP 2.
In either case, against Vehicles each Armour Penetration roll of equal to or greater than the listed value allows a further D3 to be rolled, with the result added to the total Strength of the attack. These Hits are not resolved at AP 2, but are instead resolved using the weapon’s AP value.
For example, a model with the Rending (5+) special rule that rolls To Wound against a non-Vehicle model will wound automatically on the roll of a 5+, and the attacking player has the choice of using an AP value of 2 instead of the AP value of their weapon.

When a model is allocated a Wound inflicted by a weapon with this special rule, it does not suffer only one Wound but instead a number of Wounds equal to the number in brackets associated with the specific varient of this special rule, with all of the Wounds inflicted using the same AP and special rules as that of the initial Wound. Roll to save against each Wound inflicted separately, but note that Wounds do not spill over to other models and are lost. This special rule has no effect on models that do not hae a Toughness value.