Board Thread:General Discussion/@comment-6192846-20150822000535/@comment-25932613-20160504223107

It really wouldn't explain though because at this point even if the knife is Grim the End at this point it is nothing more than an average golden blade. Mothy said only one sin vessel was a magic tool before becoming possessed by a Demon of Sin and that appears to have been the Clockworker's Doll since it was a soul cage essentially. We don't know if Grim the End could shape-shift normally or if that is merely part of what it gained the ability to do after becoming Seth's vessel. If Grim the End was a shapeshifting weapon beforehand somehow and not technically being a magic tool I guess it could work.