The Parry mastery provides damage reduction with a well-timed block and applies a Stun debuff on basic attack contact. When Parry’s ability accuracy is reduced, the damage reduction, Stun, or both, can fail. The Stun debuff is not always guaranteed even if the damage reduction triggers and it is also possible to have the Stun trigger without the damage to the Champion being reduced. This is because both halves of Parry are calculated separately.