Braska's Final Aeon. The first time I played the game, and I didn't do many sidequests and so I didn't have Anima, so it was terrible. When I played it with the sidequests, he's easier but it is still a hard battle.
FF1 - Chaos
FF2 - Emperor
FF3 - Dark Cloud
FF4 - Zeromus
FF5 - ExDeath
FF6 - Kefka various forms
FF7 - Sephiroth various forms
FF8 - Ultimecia
FF9 - Necron
FFX - Jecht (I consider the YuYevon fight to be the storyline wrapup, not a boss boss)
FFX-2 - Vegnagun
FFXII - Vain
FFXIII - Orphan
FFXIII-2 - Cauis Ballad
LR:FFXIII - Bhunivelze
FFTactics - Altima
Other
Braska's Final Aeon. The first time I played the game, and I didn't do many sidequests and so I didn't have Anima, so it was terrible. When I played it with the sidequests, he's easier but it is still a hard battle.