This is a fairly normal, spiked metal club (treat as a footman’s mace). The metal is a rare alloy native to the plane of Baator. It is as strong as steel, but functions as cold iron against extraplanar creatures to which that metal is inimical. Against Tanar’ri, specifically, it is particularly feared—the sight of a weapon of this material forces an immediate (unmodified) morale check as soon as the weapon is presented.