Penance (Final Fantasy X)

Penance is the name of an extremely powerful optional boss in Final Fantasy X (International version only). It appears to be a machina that is released after the ten Dark Aeons, who are also powerful optional bosses, are all defeated. It boasts the in-game record of 12 million hit points, high stats, elemental absorptions and powerful attacks, making it what might be considered the most dangerous boss in the game (and some say the entire Final Fantasy series). It is accompanied by its two arms in combat which have their own powers, including regenerating a few rounds after defeat. Depleting this boss' hit points can take around one full hour. Despite it being the single most powerful enemy in the game, it can be felled by the auto-kill Zanmato attack used by the Aeon Yojimbo.

Note that in the original Japanese version of the game, Penance was known as Der Richter, which loosely translates from German as "The Judge" or "That Judge".