Apocrypha Generator

The Apocrypha Generator is a large device constructed by Egil within the Mechonis. When activated, it produces waves of ether that permeate across the Mechonis. These waves are designed to counter the natural wavelengths of the Monado's ether, which prevents the weapon from being activated and renders it useless. It is possible for the wielder of the Monado to overcome the Apocrypha Generator through sheer will, raising the power of the Monado's ether waves so the Apocrypha Generator cannot cancel it completely. This is naturally more taxing than simply using it as normal.

As a gameplay element
Egil activates the Apocrypha Generator before he faces the party in the Fortress Depths. Shulk cannot use his during this battle, nor any subsequent battle, until he successfully forces the Monado active at the Ulna Passage. He remains able to auto-attack and use other arts unhindered.

As a location and boss
The Apocrypha Generator is located within its own chamber, where it defends itself from being destroyed by the party. Upon being destroyed, Shulk unlocks.