Since we're talking about FFX, and I did have a dream about the final bosses before this. (Strange dream though, as after Jecht, instead of Yu Yevon, I fought Vayne Solidor)

As much as I love to hate Seymour - who doesn't? - it is made super clear eventually that Yu Yevon is the ultimate baddie. He created all the conditions that made Seymour and Jecht what they are. He created Sin, and the final Aeon, and that's bad, mmmkay?

Oops. I voted other as I mistook villain with antagonist for a second. After all, since it's a game with two protagonists, it's also a game with two antagonists.

But main VILLAIN, it's Yu Yevon. In a similar way that Zemus/Zeromus is to FFIV. It's made very clear from the whole pilgrimage thing as you dive deeper into that.

He pretty much is, but some have debated because he is no longer sentient at this point.

Jecht of course is considered main antagonist, at least to Tidus, but Yu Yevon is the one behind Sin and the central conflict.

And do you need to be sentient to be the main bad guy? I don't think so, especially because that was a consequence of him creating and constantly reborning Sin. He was human once, did something that changed the world forever for the worse, and as a consequence lost his humanity.

Uh, suddenly this description is sounding like Hojo.

Hojo at least felt like a character. But yeah, Seymour's threats are secondary to Yu Yevon's, and while main antagonist to Tidus, Jecht isn't evil

You know, although Yu Yevon was the one that created Sin and lead to the world of Spira being caught in such a spiral of death, we can't let Bevelle go off free.

First, Yu Yevon summoned Sin to fight against Bevelle 1000 years ago from when the game starts. And it kinda worked, I suppose, the war ended, but so did Zanarkand, and thus Bevelle kinda got a free win, I guess you could say.

Second, with Sin now a constant threat, Bevelle posed as the good guys, creating a religion out of what was its enemy once, and even stealing what was a song against them and transforming it into something that instead "praised" them (not exactly praised, but you got what I mean. And the song I'm talking about is the Hymm of the Fayth, Macchen explains its origins when you get to Mt. Gagazet, and knowing it gives a whole different meaning to the moment where the Al Bhed destroy their Home, as it now not only are they grieving the dead and their lost home, but basically declaring war on Yevon). Plus, this religion they created was full of lies, assimilited or condemmed minorities (we can see the Guado and Ronso are with Yevon, whereas Al Bhed are against, but who's to say it was always like that?) and manipulated people into following its ways throughoutly, being thus the main cause behind why Spira has been stuck in such a devious cycle for so long.

Third, and now this is a bit more related to FFX-2, but whatever, Bevelle literally had a living weapon that could destroy the world, Vegnagun. Shuyin tried to use it so that Lenne, a summoner and his lover, didn't have to die because of the war (they're both from 1000 years ago), but got found by Lenne and then both got cornered by Bevelle soldiers who killed them. Now, compare Sin, who, yes, destroys cities, kills a lot of people, but can still be somewhat tamed and calmed (even though that also depends on who's his current fayth), and, even though it's at the cost of two people, can be put to rest for some years, to a living weapon that destroys the world in seconds. I believe the first option is somewhat more preferable to live with than the second, at least you might still be able to enjoy bits of the world with one which you definitely can't with the other.

You see, I guess you could say the true bad guy of FFX is none other than Yevon, somewhat started by Yu Yevon and his creation of Sin, plus his daughter Yunalesca and her defeat of Sin, but who really created a religion out of this was Bevelle, just to get a "good guy" reputation. It is kinda questionable how and why Yunalesca decided to side with what was once the enemies of her nation, but I guess that she, as a dead person, couldn't care less about how many people died with the continuous defeats and revivals of Sin.

Square grabbed a rather sensitive topic, religion, and created a game with huge focus on it, and you can't deny that many, to not say all, religions of the world have their own contradictions and questionables acts, and none are free of them. Even if they pose as something safe and that you can confine in, their past and secrets aren't really sunshines and rainbows. This is the bigger criticism that lies in FFX and Square transformed it into its "bad guy".

Don't get the wrong idea, I'm not saying Yu Yevon should be forgiven or isn't the bad guy. Not that. I'm saying Yevon, both Yu Yevon and the religion that came out of his actions, is the real main villain of FFX.

Yeah, Yunalesca and others created the hypocritical religion and kept the cycle going. That's kinda where "Other" option in the poll fits in. There's definitely multiple big villains of the game who each pose their own threat, though Yu Yevon and his incarnations of Sin are the primary threat.