101Leafy researched the games.
Bone Horn+

An enormous Hunting Horn. Its tone inspires hunters to unlock the power within.
| Class | Hunting Horn |
|---|---|
| Rarity | 4 |
| Attack | 884 |
| Defense | +10 |
| Slots | 2 |
| Price | 5,040z |
Upgrades
| Upgraded from | Bone Horn |
|---|---|
| Upgrades into | Hunter's Horn |
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 730.