Fiend Colony
From Final Fantasy Wiki
The Fiend Colony is an optional dungeon in Final Fantasy X-2. It is located on the Mi'ihen Highroad. You must dispatch a level four or five Chocobo to the highroad from Clasko's Chocobo Ranch during Chapter 5 to access it. Once it returns, Clasko will report that a new dungeon has been found.
To travel through this dungeon, you will need to destroy stone walls with bombs. Near the entrance, you find some S-Bombs, and fighting random battles will get you more. Some walls are stronger than others, requiring you to use M-Bombs or even L-Bombs. There are fake walls, however, and if you try to destroy one of them, you will have to fight an Epitaph.
Once you reach the back of the cave, you will have to fight King VERMIN!. After he is defeated, you are automatically taken to the entrance to the colony, and all the walls are reset. You also receive the Font of Power Garment Grid.
Many of the enemies here, such as the Hug Bug reappear in Via Infinito. Scanning one of these fiends reveals the Fiend Colony to feature a complex social hierarchy.
