This nondescript brass horn is actually a magical item created on the Upper Planes. Similar to the attack of the Baku, it inflicts damage on evil creatures when blown.
Source: The Planewalker's Handbook, page 137
- 554 reads
Planescape, Dungeons & Dragons, their logos, Wizards of the Coast, and the Wizards of the Coast logo are ©2008, Wizards of the Coast, a subsidiary of Hasbro Inc. and used with permission.