When you're wearing the mask, you'll be able to see (and therefore kill) the Fire Elemental that is guarding the tomb of King Strohm. Since you were already wearing it you probably didn't notice, but without the mask it attacks you and you can't defend yourself. You can keep it and use it as a helmet for mages or thieves (it protects against critical hits)
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Melusine
Your voice is ambrosia