Final Fantasy XII: The Zodiac Age - Windvane Side Quest / Boss: Earth Tyrant

You can start this sidequest after the events at Raithwall's Tomb, but I... kinda forgot about it until that point, resulting in me being way overpowered for the fight.
The quest is fairly simple, just requiring you to go around, talk to a few NPCs in Rabanastre, get an item in the Westersand and returning to the city. The fight is the only somewhat challenging part.
The Earth Tyrant is weak to Wind and absorbs Earth, its attacks can Poison your party, but he's otherwise an oversized Wild Saurian, you can Slow and Blind it to make the fight easier as well.
A word of caution though, slaying this beast greatly reduces the number of sandstorms in the Westersand, which can be detrimental if you have anything to do with the Gnoma Entites, such as stealing their items, so you might want to wait until you've done all that before completing the quest.