After you defeat Boomer, Chandeli-HO takes you to the top of the keep, where you finally face the giant sword, Exor.

Defeat Exor

Exor consists of the Exor (the dots at the top of the screen), the Left Eye, the Right Eye, and the Neosquid (mouth). If the mouth is defeated, it opens wide. You can't damage Exor until you defeat one or both eyes. The eye gets a swirl pattern in it when it is defeated and no longer protecting Exor. However, the eyes can come back to life. When the eyes are alive, use multi-target attacks whenever possible. If one or more eye is defeated, hit the Exor.

The mouth can cast Flame Wall, Aurora Flash (which can inflict Sleep), Static E, Water Blast, Corona, and Solidify. It can hit single characters with Carni-Kiss, Lulla-Bye, and Flame Stone. The eyes can cast Venom Drool, Bolt, Mega Drain, Gunk Ball, S'Crow Bell, and Flame Stone. The eyes can also cast Dark Star on a single character for high damage, and can do a regular attack on a single character.

After the battle, Exor sends you to The Factory.