Corvus Glaive does not take damage from Cold Snap, Bleed and Shock Debuffs, nor Frostbite, while Glaive’s Immunity is active. When Glaive’s immunity reactivates or is disabled, those Debuffs are Purified and Corvus takes damage.
At the start of the fight, Corvus gains 20 permanent Glaive charges, granting him True Damage and guaranteed Critical Hits with his glaive as long as Glaive’s Immunity is active. A charge is spent every time Corvus hits with Basic Attack using his glaive.
Corvus’ blade is damaged after he uses all of his Glaive charges, disabling Glaive’s Immunity for 50 seconds. Corvus cannot inflict Critical Hits while Glaive’s Immunity is disabled.
When Glaive’s Immunity reactivates if Corvus has 0 Glaive Charges, he regains all of his Glaive charges.