Yiazmat

Yiazmat is not only the hardest secret boss in Final Fantasy XII, but the hardest in the entire Final Fantasy series. He is a large magical dragon who is the forty–fifth and final target in the game's hunting campaign, whose petition was submitted by none other than Montblanc, the person who runs the hunting business. It is revealed that Yiazmat killed the master who taught Montblanc everything he knows, and the real reason he set up the hunting business in the first place was to find someone strong enough to finally kill the most fearsome beast in Ivalice.

Yiazmat has FIFTY MILLION HIT POINTS. To give one a perspective, the final boss of the game, in all his forms, has less than one million hit points. Yiazmat is so powerful that one health bar that stretches across the whole screen isn't enough for him, so he has fifty, each representing one million HP. The fight will take well over an hour even at the highest level.

Yiazmat is named after Square project director Yasumi Matsuno, who left the company during FFXII's development. This is both an insult (since Yiazmat is an evil monster) and a show of respect (since Yiazmat is the most powerful evil monster in Final Fantasy history).