The Bramble Blade

(From here.)

The Bramble Blade was forged by the fey to slay goblins. As it gained sentience over the millennia it began to realize how low it’s purpose is, and how the simple act of it’s creation was a call for genocide out of hatred and ignorance and xenophobia. This has driven it mad and shifted it’s enchantment to the murder of fey creatures. It begs to slay fey whenever they are encountered, going so far as to pretend to detect lies or evil (which it cannot) and trick wielders into killing anything of fey origin.