Final Fantasy X

[Don Flamenco]

Is there any point in time where I have to use all characters?  'cause I just want to ditch Kimhari... spoilers are fine. 

[demi]

No

[magus]

quite ironicaly there is a boss fight where you are forced to use khimari only but apart from that,not that i do remember... (altough you are always forced to a tidus,rikku,wakka party for every underwater fight)

[TakingBackSunday]

Well early in the game, you kinda have to use everyone because of their particular strengths against certain enemies.  Once you start to seriously cover the sphere grid, though, some characters ccan be phased out.  But on the topic at hand, other than a few Yuna-mandated fights and a Kimhari Mt. Gozel (was that the name of that place?) boss fight, you can use whatever.  I never bothered with Riku, she sucked.  Tidus, Auron, and Wakka/Lulu ftw.

[magus]

yea tidus,auron and wakka was my party too altough i'm pretty sure you can make a better party for the dark aeons and optional boss,wakka is still necessary simply for his ability to hit 12 times in a row with his limit

[Don Flamenco]

what are the secret bosses in this one?  or was that only in FFX International...

[magus]

i'm not sure about the US version but international is the same as FFX PAL version
basicaly you get to fight dark version of summon that feature like millions of HP,the first summon are somewhat doable even on normal level (valefor) but the deeper the go,the more grinding involved
if you beat all of the summon you get a huge boss called penance which features 12 million hp and an attack that can possibily insta-kill your entire party if you give him the chance

you can also unlock extra boss fight by catching enemies using special weapons,they are necessary if you want to do dark aeons because for every extra boss fight,you get +4 stat putting sphere which are essential to max your stat

[demi]

what are the secret bosses in this one?  or was that only in FFX International...

There's a super monster in the fighting arena. International had the Dark Aeons, and Penance