In Hindu mythology Asuras we’re a type of… not good divine beings (though not uniformly evil). There’s no clear conceptual parallel like a demon or anything. Instead they are simply immensely powerful beings with a higher cosmological role than humans. Think Demi gods, superheroes, giants, etc.

Soooo maybe this mirror has an asura trapped in it. Or the mirror can give a person the powers like an asura. It’d be the equivalent of somebody stealing a briefcase nuke, or taking the keys to a one of the world’s most dangerous prisoners.