Gyrfalcon's Hauberk

After you emerge from invisibility, your Void weapons gain Volatile Rounds for a short time.

If you defeat a combatant with a finisher while invisible, every weapon gains bonus damage. You and nearby allies receive a reserve overshield and better class ability regeneration, and those overshields can be used by activating a class ability.

It rewards a stealth-and-finisher loop on Void Hunter, where invisibility comes from dodges and melee.

The reserve overshield lets you hand protection to the team before a push.

The reserve overshield is stored until a class ability is used, so the team decides when the protection is deployed.

• Gyrfalcon's Hauberk, Exotic chest armor for Hunters, added to your account.
• Stat Options: None, High Overall Stats (65+), or one of High Health Stat (25+), High Melee Stat (25+), High Grenade Stat (25+), High Super Stat (25+), High Class Stat (25+) and High Weapons Stat (25+).
• Extras: Use My Exotic Ciphers, when the order should spend Exotic Ciphers you already own.
• Quantity (values 1 to 15).

• An active Destiny 2 account that owns The Witch Queen, since the game data marks Gyrfalcon's Hauberk "Requires Destiny 2: The Witch Queen" on Xûr's offer of it; Destiny 2: The Collection includes it.
• A Hunter character to wear it, since armor is class-locked.

Does the damage bonus apply to every weapon?

Yes, after an invisible finisher kill all your weapons gain bonus damage.

How are the overshields used?

They are reserve overshields, deployed by using a class ability.

Where does Gyrfalcon's Hauberk come from in the game?

Exotic Armor Focusing is the source the game data gives for it, and Bungie describes Exotic Ciphers as usable for focusing Exotics at the Cryptarch.