The battle horn can be found while participating in the Invasion of Falador event. Blowing the horn increases damage to the Invasion of Falador knights, improves effectiveness when sabotaging catapults and healing soldiers, and increases experience by 25% and commendations gains by 50% while doing so. The buff lasts for three minutes. The horn is consumed in the process.
After completing the Banner of Farradorn miniquest, the horn's effects become permanent and no more horns can be obtained.