You can find the three initial EX dungeon Gates in the Girl’s Tearoom. The Gate to the left takes you to EX Dungeon C, the Gate in the middle to EX Dungeon B, and the Gate on the right to EX Dungeon A. You can complete these in any order, although EX Dungeon B may be slightly easier compared to the other two. Each of the initial three EX dungeons consists of four areas, with a Save Crystal and a boss Mirage stack on the fourth floor. Clearing all three bosses unlocks the fourth and final post-ending dungeon, EX Dungeon Z (its Gate appears to the left of the EX Dungeon C Gate in the Girl’s Tearoom).
Your primary objective in each dungeon is to reach the fourth floor’s Save Crystal, since Save Crystals give you infinite HP/AP restorations and access to your Prism Case. From there, you must defeat a challenging boss stack. Once you’ve defeated the boss of the dungeon, an Exit Gate appears behind them, allowing you to travel back to Nine Wood Hills.
In-game maps are not provided in any of the EX dungeons, so refer to the accompanying maps to find your bearings. Fortunately, most of the areas are short, and the layouts should be familiar to you because they’re clones of locations that you visited in the main story. The challenge of these dungeons revolves mainly around the high-level enemies and boss encounters, so you may end up investing a significant amount of time into leveling your Mirages while exploring the dungeons.
An efficient strategy for leveling your characters and Mirages is to reach the fourth area of an EX dungeon, and then stick around the Save Crystal while fighting enemies. After each battle, you can simply approach a Save Crystal to completely restore HP and AP, then continue fighting and leveling up. You can make this process faster by preparing your stacks with strong elemental “–ga” spells of that floor. For instance, you can expect several bomb-type Mirages in the third area of EX Dungeon C, so prepare your stacks with Waterga spells to quickly dispatch the groups of enemies found there. Since you essentially have infinite HP and AP at the Save Crystal, you never have to worry about running out of potions and ethers.
An extremely convenient way of reaching EX dungeon Save Crystals safely is to equip the Stealth mirajewel (found in a chest on Big Bridge—Segment 2) and have a Mirage with the Flee ability in one of your stacks. Flee can be unlocked on the black chocochick, cactuar, and cactrot Mirage Boards. While traversing an EX dungeon, you can flee from every single random encounter until you reach the Save Crystal, where you can then set up camp and level your party. Remember to unequip your Stealth mirajewel during the leveling process, though, as it reduces your chance of finding enemies. To find enemies even faster, equip the Lure mirajewel (found in the Phantom Sands—Toil 3).
Another feature of these dungeons is the inclusion of the kraken, buer, tiamat, and asterius Mirages (Crystal Tower “mini-bosses”) in the potential random enemy encounters. These mini-boss encounters are particularly dangerous and can be resource-consuming, so it’s advisable to simply flee from them if you can.
If you want to fight your way through the dungeons, make sure to bring plenty of hi-potions, ethers, and hi-ethers with you on your climb to the Save Crystal. Also, plan ahead by reviewing the enemies list and map information following this text, and bring Mirages that you may need (for support abilities, elemental resistances, and puzzle switches).
Additionally, it’s highly recommended that you have access to the Death spell or a Death-inflicting ability. Many of the high-health Mirage stacks encountered in these dungeons are weak (or at least vulnerable) to the Death effect. A successful Death cast on these stacks can make your dungeon crawl much less stressful!