101Leafy researched the games.
Khezu Horn

Made to look like the mouth of a dreadful Khezu. Shape and tone are unforgettable.
| Class | Hunting Horn |
|---|---|
| Rarity | 3 |
| Attack | 624 |
| Thunder | 200 |
| Slots | 1 |
| Price | 2,790z |
Upgrades
| Upgraded from | Atlas Hammer |
|---|---|
| Upgrades into | Khezu Horn+ |
Can also be made new at the smithy.
Upgrade tree from モンスターハンターポータブル 2nd G 公式ガイドブック (Enterbrain, 2008), page 738.
Materials
Flabby Hide ×5, Electro Sac ×4, Machalite Ore ×6, Lg Monster Bone ×6