The mounted sword is purely decorative and is a way of showing that the player has completed Merlin's Crystal. When the mounted Excalibur is removed from the wall, the sword is returned to the player's inventory. An enhanced excalibur cannot be used to build this. If one already has the enhanced version, they will have to destroy it to obtain a regular one from the Lady of the Lake, mount it, and then retrieve a new enhanced one if they fancy.