Yiazmat is the secret boss in Final Fantasy XII, and well-known for its ridiculously high amount of HP. He is a large magical dragon who is the 45th 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 50,000,000 hit points, making him the monster with the most HP in the entire series. 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 50, 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.