Vouch....
50 mil hp is rediculous.
4 hours of my life on one battle, LAME!

startin ffx international to take on penance, so idk how good bad that ones gonna be yet

hell yeah

the 50Mil hp isnt the problem its having a backup team able to take over in case he spams his on hit ko attack lol
but 50mil is easy to wipe out with 2 attackers and a mage just get 2 Yagyu Darkblades for Yiazamat is weak to darkness damage so you can spam hit him for 8k+damage and with combos knock out a mil in 5 mins or less

and for the second team just full HP gear and have them cast Araise on your main team then cure/buff and use the main char to "Kite" (run laps around the outside of the arena you fight in with Lure up) and can drop him in under 2 hours

IMHO the hardest is DEFINATLY FF7 Sephiroth on a Low lvl complete chalenge (aka beat final boss under lvl 30) without useing Omnislash or Knights of The Round other wise in normal game play hardest boss i would have to say is FFXI pre Rise of the Zilart Shadow Lord.

caped at lvl 50 and was NEVER beaten before the RotZ expansion nuff said

and from non MMORPGS

probably FF7 Emerald weapon if you try to kill with out KoTR Mime castings lol

If you throw in a ton of limitations any boss is going to be the hardest

you have to traine longest if you want to be able to beat penance. so he must be the hardest boss. no boss in final fantasy is hard if you just take your time to train. but he requires the most training

Penance
Yiazamat wasnt even tough, just took a little time to beat