Penance is the hardest boss in FFX. He appears only in the FFX PAL versions which were released to European and Australasian countires and also in the International version.

In the Japanese and NTSC version, the only enemy you can fight that does more than four digits of damage in Nemesis. In the PAL and International, there are about 10.

To fight Penance, you need the prerequisite of fighting all the Dark Aeons first. Even though they do a tonne of damage and are really really fast and some are just so damn annoying (Yojimbo..) it's pretty much a matter of preparation.

For Penance though, you need some awesome stats and abilities. Quick Hit every turn is your only hope of surviving.