Board Thread:General Discussion/@comment-5634526-20141008124905/@comment-12459636-20141013040111

Sounds very possible. If Lumiere is to be believed, the very first Dark One was some kind of demonic creature made of darkness. Maybe Yensid forged the dagger to keep it under control but his apprentice took his hat and the dagger and ended up becoming the Second Dark One, thus creating Rumple's curse.