Talk:Sin of Wrath/@comment-206.53.152.166-20131014002929/@comment-6192846-20131014005140

The Daughter of Fog is all the direct proof you need. It's very explicit that Yvette "played" with its abilities at shape-shifting. The key turned into the knife when she became enraged by her father's plans to murder Gast and her own helplessness to stop him.