Oh, I'm pretty sure I've got this one. The Black Waltz's.

Verse 1 - I'm here to get the princess - That's what BW 1 said.
Verse 2 - I'm following the same - Pretty much the same as one.
Verse 3 - I'll take the princess -dead or alive-
but now I've fallen, oh I've fallen. I've fallen, I'm slain but I'll not give in yet. I'll run on pure disdain for that maiden of the minuet.
Three was going to take her anyway possible. Then he gets his butt handed back to him and appears a second time.

^ That's gotta be it.

At first I thought PS was screwing with us.
But I look at it now and it makes total sense.

I'll get Pretty Soldier for you.

Sigma got the correct answer first.
So ask the riddle.

From death I come to spread my evil.
With my eye to stare you down.
If I should win, I'll take you to my level.
If I should die, then the toys should cease.

Garland and his airship
I mean it looks like an eye and it definitely brings death to many, even the black mages as synthetic life.

Nope, sorry.

Is it Necron

But I'm thinking a boss that has to win automatically like Beatrice or Ultimate Kuja

Noperoonies, Progamer.

Garland?
Didn't he say something about killing the Black Mages

Non, mon bon BP.
It's a Creature.

Kuja

Atomos
It's the one eyed summon that was used in an FMV
It destroys a lot of the Black Mages

Nope, neither of them. Sorry, ladies.

And it wasn't Garland airship? The "EYE IN THE SKY"?