[kupoartist]

(sorry ... I'll help you a little Macceh ^_^)
FFVII's is "One Winged Angel", with Latin lyrics that are just repeated a lot... but Very good ^_^

FFVIII has at least 3:
"The Legendary Beast" (Plays when Ultemica summons Greiver) - Starts like the Jaws theme or somthing ^_^ , develops intoa great Marching style thingy.
"Maybe I'm a lion" (Plays when Greiver is defeated, and Ultmetica junctions with him) - Starts a little slow, ends up as a sort of Rock song. A bit similar to the "Melody of Coruption" in FFIX...
"The Extreme" (Plays in the final time compression phase) - This one starts with a distorted Rendition of "Fithos Lusec Wecos Vinosec" (- Succesion of witches I believe), then develops into a fast paced "Witchy" version of the classic battle theme
(these are easily the best of the FFVIII OST, which is pretty mediocre otherwise)

FFIX has two in a way.
It has the Kuja fight's "Messenger of Destruction" (very similar to the "Melody of Corruption") which is an excellent Rock style battle theme.
And it also has the lengthy "Final Battle" (inspired title ^_^). Which is fast paced and pretty damned cool. Also i swear I can hear some of the "tormented souls" in the background puking up

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Anyways ^_^ : My favorite is either "Messenger of Destruction" or.... Kumi Tanioka's "Awakening". Except theres a problem with the later, in that its on the FFXI OST, so I don't even know its a "Final Boss" theme. (and FFXI probably wouldn't get a final boss anyway :/)