I was just in a discussion about how FF bosses have multiple forms, and this just sprang to mind. Villains having Final Forms seem to work best when it is clearly set up. Neither World of Chaos nor Xemnas's Dragoon seem to be. Same with Marluxia.

Simply, it was a giant ass boss that Sora had to blow up awesomely, that's all the plot relevance you need.

 

... That, and it was probably a manifestation of Ansem SoD's Darkness and the power he'd gained by stealing a few of the hearts of Worlds. We know he did this because not only does everyone make it painstakingly obvious that the world's hearts are fading into darkness "Oh look, a Star's going out!" Thanks Goofy, but we can also see all of these "World Hearts" being released back into the universe during the ending scene of KH1. In other words, the pretty Star shower that was actually important while everyone was crying at Sora and Kairi getting separated... again.

 

So yeah, World of Chaos = Ansem SoD + Power of Planet Sized Hearts consumed by darkness.

Well, World of Chaos is actually a fuller manifestation of Guardian. He and Ansem SoD are linked, hence Ansem acting as a host and Guardian as the symbiotic creature. In most of the Ansem fights, their bond is only implied, but in that particular battle, Ansem was able to use a copious amount of Darkness to reveal their true, disturbing relationship. A literal illustration of Guardian's parasitic nature. Hence, why he is literally attached to Ansem during that fight.

 

 

(Info from KH wiki)

Edited February 13, 201510 yr by Pandy Monium

I honestly don't recall a single FF boss' final form being set up other than chaos in FF1 and kefka in FF6, but as for world of chaos, yeah like oblivion 22 said, it's just an amalgamation of all of the darkness ansem SoD had at his disposal especially since they were so close to the dark realm. As for marluxia and Xemnas, we'll both of their final forms are machines, it's not out of the question that they themselves could have built it. If they can build an artificial kingdom hearts it can't be too hard to build a battlestar class transforming castle.

FFXIII had the final form set up quite a bit.

at the same time xibar and the cannon tank at the beast tower is equipped with FF

 

Edited March 5, 201510 yr by Weedanort

Because Final Bosses always need to blow up

Well the Dragoon came from the power Xemnas absorbed from the damaged Kingdom Hearts.

And Marluxia... I dunno? Maybe just a manifestation of his power?  He was planning on taking over the Organization so I guess it's safe to assume he has a ton of power to... uh... make a final form? I'm just making crap up for him I have no idea