Source: Bigby Presents - Glory of the Giants

Wondrous Item, Rare

This brass war horn is engraved with the war rune, which glows purple when the horn is blown.

You can blow the horn as a bonus action. When you do, if you have the frightened condition, you immediately end that condition on yourself. You also have advantage on saving throws against being frightened until the start of your next turn.

Invoking the Rune. When you blow the horn, you can also invoke the rune, imbuing the horn’s deep call with protective magic that affects creatures of your choice within 30 feet of yourself. You and all affected creatures gain a +1 bonus to AC until the start of your next turn.

Once the rune has been invoked, it can’t be invoked again until the next dawn.