The Horn is a tool, which also can be used as a weapon, given to the player after defeating the Corn Boss. It lets off a loud, foghorn-like sound that can activate secret areas and events. The Horn can also deal small to moderate damage to a nearby enemy, also knocking them up in the air. This weapon has unlimited use. After activating the Horn, but before the noise is made, the player can change its pitch by pointing the left thumbstick in a different direction. It is required to open the entrance to the Flooded Temple, making it a vital tool.
- Makes Hawkster appear during the Tall Grass Field level.
- Makes BiPolar Bear appear during the Snow World level.
- Opens the entrance to the Flooded Temple level.
- Damages enemies and knocks them down.
- You can open the locked door at the end of the Animal Ark with the horn if you have the Key Sword in hand.
- There exists a save glitch in which the Horn won't be saved while in Multiplayer Mode. The Horn may appear to be saved after defeating the Corn Boss, but it will disappear soon after restarting the game. If the Horn has disappeared from the inventory after reloading the game, then the Corn Boss must be defeated single-handedly in One Player Mode.
- If you equip the Horn on Normal Mode then switch over to Insane Mode without switching items, you can use the horn to open the door to Flooded Temple without passing through the Marsh or Corn Boss levels. This can be profitable if you're trying to unlock the Cult Minion, as Marsh is one of, if not the hardest level in all of Insane Mode. You will not be awarded a Gold Skull if you skip the Corn Boss, however.