With the speed of the higher level "Call the X's Blade" and mutable abilities, you basically give them a "Bane(Whoever you are fighting)" ability at the higher levels (12+ ?). That seems a bit wrong...

OTOH you might want to throw the ability to declare one material that it emulates on their too for the 8th level one (Alchemical Silver or Cold Iron basically, since hardness 20 basically means it is already as good as adamintine...right?).