You can use an action to blow this horn. In response, warrior spirits from the Abyss appear within 60 feet of you. These spirits look like minotaurs, and use the berserker statistics. They return to Abyss after 1 hour or when they drop to 0 hit points. Once you use the horn, it can't be used again until 7 days have passed.
The horn summons 3d4 + 3 berserker. To use the horn, you must be proficient with all simple weapons.
If you blow the horn without meeting its requirement, the summoned berserker attack you. If you meet the requirement, they are friendly to you and your companions and follow your commands.
If you have proficiency with a given musical instrument, you can add your proficiency bonus to any ability checks you make to play music with the instrument. A bard can use a musical instrument as a spellcasting focus. Each type of musical instrument requires a separate proficiency.