The Mechonis Core is where Egil went after defeating the party in Agniratha and fusing Yaldabaoth with the Mechonis itself. The Core is where the final fight between the party and Egil takes place. Once Shulk and Egil reach mutual understanding, Dickson reveals himself as Zanza's disciple and shot Shulk in the back to release the God from within Shulk's body.
Zanza and Meyneth, still inside Fiora, fight over the now headless Mechonis. Meyneth eventually exit fiora's body to shield the party and is killed as a result allowing Zanza to steal her Monado. The whole area and the Mechonis is destroyed as Egil stays behind to protect the party while they are escaping.