I had Mirrex in my hand and my opponent (Mage) played a Treacherous Tormentor and discovered the dark gift Sweet Dreams (+4/+5 and put on top of their deck.) They chose Li’Na Shop Manager, if it matters.
My Mirrex turned into the Treacherous Tormentor, and then it was shuffled into my deck. I’m not sure why my copy of the Tormentor would have shuffled itself.