Wondrous Item, Legendary (Requires Attunement)
This beetle-shaped medallion provides three benefits while it is on your person.
Defense. You gain a +1 bonus to Armor Class. Preservation. The scarab has 12 charges. If you fail a saving throw against a Necromancy spell or a harmful effect originating from an Undead, you can take a Reaction to expend 1 charge and turn the failed save into a successful one. The scarab crumbles into powder and is destroyed when its last charge is expended. Spell Resistance. You have Advantage on saving throws against spells.
Source: SRD 5.2.1 · CC-BY-4.0