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This horn appears to be a normal trumpet. It can be sounded as a normal horn, but if the command word is spoken and the instrument is then played, it deals 5d6 points of sonic damage to creatures within a 40-foot cone and causes them to be deafened for 2d6 rounds (a DC 16 Fortitude save reduces the damage by half and negates the deafening). Crystalline objects and creatures take 7d6 points of sonic damage, with no save unless they’re held, worn, or carried by creatures (Will DC 16 negates).
If a horn of blasting is used magically more than once in a given day, there is a 20% cumulative chance with each extra use that it explodes and deals 10d6 points of damage to the person sounding it.