Amplify Shields, when filled, add a bonus amount of Amp Damage to the next shot (called an Amp Shot) fired from any projectile weapon, at a cost of a certain amount of shield damage (the shield's Amp Shot Drain). They are thus well suited to longer-ranged character builds where they can be allowed to recharge between shots and there is little risk of taking damage.
An Amplify Shield is essentially the opposite of a Roid Shield.
As rarity increases, the amp damage increase, while shield recharge delay and amp shot drain decrease.
The Bee – Legendary amp shield with low capacity, high amp damage and zero amp drain.
Borderlands: The Pre-Sequel
Rerouter – Legendary amp shield with high amp damage, high amp drain, and heals for an equal amount of amp damage when an amp shot is fired.
As of November 14th, 2012, Gearbox released Patch 1.2.0 for Borderlands 2, Which added a balance that caused Amp Damage to be divided evenly among multiple projectiles rather than added to each, and added a bug fix so Amp Damage no longer applies to every round remaining in a thrown Tediore weapon, significantly reducing this shield type's former effectiveness for close-range character builds. Splash damage from explosions caused by a weapon's projectiles do receive the full amp bonus though, regardless of how many projectiles are fired, and guns that fire multiple projectiles but don't have a damage multiplier in the item card will have each projectile get the full amp bonus.
Amp Damage is not further divided on shotguns with an accessory that increases their pellet count. This is most evident (and effective) on shotguns with lower pellet counts.
The common amplify shields is obtained randomly from any suitable loot source.
Amplify damage is added before calculation of critical hit damage. This makes weapons that give a bonus to critical hit damage especially powerful.
Amplify damage is also added before calculation of elemental damage bonuses. Thus, hitting a target with the corresponding elemental type will multiply both gun damage and amp damage.