Master’s Amulet

Every shield guardian has an amulet magically linked to it. A shield guardian can have only one corresponding amulet, and if that amulet is destroyed, the shield guardian is incapacitated until a replacement amulet is created. A shield guardian’s amulet is subject to direct attack if it isn’t being worn or carried. It has AC 10, 10 hit points, and immunity to poison and psychic damage. Crafting an amulet requires 1 week and costs 1,000 gp in components.

A shield guardian’s solitary focus is to protect the amulet’s wearer. The amulet’s wearer can command the guardian to attack its enemies or to guard the wielder against attack. If an attack threatens to injure the wearer, the construct can magically absorb the blow into its own body, even at a distance.

A spellcaster can store a single spell within a shield guardian, which can then cast the spell on command or under specific conditions. Many a wizard has been rendered helpless by enemies, only to surprise those foes when its shield guardian unleashes potent magical power.

Source: Monster Manual p. 271