So, now that we've reached Xande, I can offer my own idea about him without having to worry about spoilers. And yes, the fact that there was really nothing more to him would have been a spoiler in itself.
Anyway, with the multitude of clones laying around in the final dungeon, my idea was that Xande was, actually, a monster like Doga and Unei, and what Noha did was actually turn him human; as for the why, my two big ideas, which actually work together, are that (1) Noah believed Humans get to some form of happy afterlife, which he thought would be preferable to the eternal cycle of reincarnation Unei and Doga are forced into, and (2) that becoming actually human would offer some possibilities to make experiences that the human disguise the others wear wouldn't allow - on the ground that he thought his best student would enjoy having the chance to make other experiences. It feels like the correct amount of cruelty resulting from paternal benevolence that would best fit my read of the situation.
In any case, I do think that the failure to update Xande at all was one of the DS version's biggest mistakes; there's the root of an interesting character here which just needs some good writing and development to be made into one of the most thought-provoking villains in the series, and instead the rewrite was wasted into give individuality to the protagonist group, a much harder and less necessary task, since the group as a whole has actually more characterization than the FFII team did, even if that characterization is shared among the whole team rather than each member having their own personality. Don't get me wrong, a level of rewrite that actually did give the individual group members an identity would have been great, but it would have taken a lot more work than what the DS remake put in, whereas, if the same amount of effort had gone in fleshing out Xande, it could have done a lot for making the end of the game a more interesting experience.
And, speaking of the end of the game!
Definitely don't think any of the first six fit that description.
So, are you now ready to reconsider this position? As I mentioned at the time, I disagreed, and the first case of that is definitely FFIII; this is, in fact, often considered the Ur-example of the final boss that comes out of nowhere.
Yes, some noise was made that the darkness was a thing Xande was awakening, but nothing in the plot indicated anything of the "hidden villain" sort, and given Xande's character, it would have in fact made much more plot sense if he was planning to absorb the darkness to regain his immortality, which would have led to a perfectly traditional two-stages boss fight. There's some argument to be made that "thematically, the Cloud of Darkness being its own thing is better", but I think that argument is weak; the only reason is to allow Doga to say "Xande was manipulated" which, honestly, is a weak attempt to make the game's main villain not be the direct force, instead being just another example in the game of somebody manipulated into evil by a malicious advisor. Overall, if an edition of the game was made that didn't have the Cloud of Darkness in it, just Xande doing a transformation by absorbing the darkness in himself, nobody who played the game without knowledge of the Cloud of Darkness' existence would even be able to notice that something had been replaced.
So, overall, I remain my case that FFIII is most certainly a game which feature an eleventh hour final villain coming out of nowhere, and one of the first six games in the Final Fantasy series, demonstrating this has been a thing in Final Fantasy for a very long time.
If Desch can survive the nuclear furnace, it makes you wonder what the hell actually did the Ancients in.
The Wrath of Light; we were told this. It's like the Cloud of Darkness, only the colors are reversed.