World of Final Fantasy/Chapter 4: A Legendary Warrior

Cornelia
When you return you will be treated to a cutscene where Bahamutian Soldiers will invade the Watchplains and build an outpost. Princess Sarah says Cornelia does not have the manpower to fight them this close, so Reynn and Lann vow to clear the area by sneaking up on their leader. After the cutscene head back through town, and enter another short cutscene, where the Brigade Captain informs you that they will cover you as you enter the enemy camp and will advance upon your signal. Head out into the Cornelia Region, and take the left fork to enter The Watchplains.

The Watchplains
This dungeon is straightforward but winds around itself a bit. The guards that are fighting Goblins will give you an item as a reward if you beat the Goblin for them. Occasionally you will encounter a Bahamutian Soldier who summoned a Babyhemoth as well, killing the Soldier will free the Babyhemoth for imprisment. The Goblin-type creatures here are unimprismable until you defeat the boss, so just beat them up for XP for now.

In the second area, take the path directly ahead through the camp to reach a forced encounter and a chest, then resume climbing through the dungeon. Keep going and eventually you will be forced into an encounter with all four goblin types surrounding the Brigade Captain. There is another hidden chest just up the hill behind the tower.

Save, and proceed for a cutscene and a long fight. You will see the princess wandering and a Giant Goblin climb up behind her. Realizing that they can't reach her in time, Reynn and Lann panic, and subconsciously activate their Mirage Keeper powers to awaken the Brigade Captain into the Warrior of Light, who then immediately charges the goblin and knocks it off the mountaintop. Tama reveals that the Brigade Captain must have been a Medium, a powerful Champion lying dormant,

The bosses are nothing but damage sponges with no weakness, so you should swap out your current mirages for ones that have healing abilities such as Cure and Regen, high defense, and/or access to Protect. Unfortunately your only strategy here is going to be to hit them until they die. Nothing special about this fight.

After the fight, another cutscene plays, and we are introduced to several new characters. We see the Woman in the Cage, who announces that you've arrived. The Knight in the Black Armor asks how many years have passed, and the woman says it is difficult to gauge from in the cage. The knight says time has resumed its march. He calls out to Segwarides, the Knight in the Golden Mask, who is then told that he "may begin". The woman asks a third character, the Plumed Knight whether she will waver, who responds simply with "we have a prophecy to fulfill".

Once you regain control of your characters, don't exit just yet. First, head north to reach another chest. Afterwards, head south past the gate to the Secret Area. The Black Chocobo here can be either imprismed or killed, it doesn't matter. After the fight is over, you will get its Memento, unlocking its transfiguration space, which can now be purchased on the Chocochick's Mirage Board. If you imprismed it, you may transfigure to it without having to spend a Skill Point to unlock it. Head back through the gate and return to Cornelia.