The first battle you get into on the second disc? The truly awesome Super Dimensional Gear Yggdrasil IV, made up of the central block of the Kislev Capital versus a mobile weapon easily the size of a planet-killing asteroid.
This gets topped by how you get into the final dungeon, Merkava. It has its own, even more powerful Wave Motion Gun that can wipe out anything approaching it. While the Yggdrasil IV and Shevat's flagship Excalibur each have Deflector Shields, they could each only survive for a few seconds under Merkava's gun. So Bart comes up with a Crazy Awesome plan to handle it: have Yggdrasil IV stand on top of Excalibur, with their shields combined to maximize how long they'll last, and to get extra speed Yggdrasil IV carries a pair of old Xeboim ICBMs under its arms. Once the the ICMBs burn out, Yggdrasil IV drops them, jumps forward, and pulls off Excalibur's bow spike to use as a giant sword, stabbing it into Merkava's main gun and demolishing it. Then Excalibur blows up Yggdrasil IV, after Yggdrasil III ejects, to destroy the cannon beyond repair. All of this while Bart's gear pilots Yggdrasil III via a gear-sized nautical steering wheel, just because. It has to be seen to be believed.