Lost Crown of Besilmer

From Princes of the Apocalypse, page 223.

Description
Wondrous item, legendary (requires attunement).

This dwarven battle-helm consists of a sturdy open-faced steel helmet, decorated with a golden circlet above the brow from which seven small gold spikes project upward. You gain the following benefits while wearing the crown:
 * You have resistance to psychic damage.
 * You have advantage on saving throws against effects that would charm you.
 * You can use a bonus action to inspire one creature you can see that is within 60 feet of you and that can see or hear you. Once before the end of your next turn, the inspired creature can roll a d6 and add the number rolled to one ability check, attack roll, or saving throw it makes. This uses 1 charge from the crown. It has 3 charges, and it regains 1d3 expended charges daily at dawn.