Yes, I know there's one more boss after this one, but considering it's a storyline battle that you cannot possibly lose, I'm not really counting it.
Anyway, here it is, the final boss of Xenogears. Normally, you'd weaken him by using your entire repertoire of gears to stop four undulating "spheres" (balls) around the core. If you do not do this, you fight a suped-up version of the final boss with four times as much health and damage, he also gains the abilities of the sphere bosses, a heal, a fuel drain, a large elemental attack (of which he just didn't want to use this time) and a random status effect that can slow your gears into oblivion.
Disclaimer: I do not, nor do I claim to own Xenogears. All trademarks and copyrights belong to their respective owners. This video and all following were recorded and posted in accordance to the "fair use" policy of copyright.