The Axe Serpentis

In a turn in which a model with this special rule Charges into combat, it adds a bonus to its Initiative Characteristic until the end of the Assault phase. The bonus added to the model’s Initiative is equal to the value in brackets after the special rule; for example, a model with Sudden Strike (2) adds a bonus of +2 to its Initiative.
A model that has made a Disordered Charge that turn receives no benefit from Sudden Strike (X).

Attacks with this special rule cause Instant Death on a To Wound roll equal to the number in brackets associated with the specific rule. Roll any viable Saves against this Instant Death-causing Wound separately and before any other Wounds the attack inflicts.