The Battle Cry is a Pre-Hardmode item. It is a highly useful tool for farming mobs. Using it will cause spawn rates for monsters to increase by 10x that of its original value, or return to its standard value if the Battle Cry has been used already. It is not consumed upon use.
Mutant Mod: 2.3.1: Changed Crafting Recipe to obtainable pre-boss
Mutant Mod: .11.0: Introduced