Final Fantasy Tactics Walkthrough

One thing that will really help in this battle is if Agrias has a high move stat. Give her Move +1 and a pair of Battle Boots so she can get out of the corner quickly and make a difference. You'll also want to bring along a Chemist with Hi-Potion so they can throw items to Mustadio, since if he dies, the battle's over. Items as a secondary ability alone is alright, but a Chemist is better as Mustadio will not usually put himself in a situation where your healer can reach him directly. Priests will do better in buffing Mustadio with Shell and Protect rather than healing directly, but they can also heal directly if your item-user is blocked by the city walls. You need to keep an eye on healing, because Mustadio is no tank and skipping a round of healing could get him knocked out and cost you the battle. Stack your party stage right on the formation screen, unless you have units with enhanced Jump to get through the archway in the wall faster that way. Consider not rushing to the arch, though, until you can see what direction Mustadio is going to move, as you don't want to get completely separated from him.

Your best damage will come from the guests, while other units should likely be melee units unless you have a relatively powerful black magic user to take along.

Definitely kill the Wizards first because they've been known to cast level 3 spells in this battle, and even their level 2 spells are deadly. After that it's up to you who to kill, but it shouldn't be much of a problem either way if you have your healers in place. This can be a good battle to try to farm treasure chests and crystals, but you likely won't have time to wait them out unless Agrias and Mustadio have retreated from the main line of battle.

After the battle, Mustadio thanks you for your help and, as it turns out, he could benefit from traveling along with the group to Cardinal Draclau. He is an Engineer from Goug Machine City that can use guns, which are relatively unknown in Ivalice. He avoids the question of why he was being chased until Agrias puts it in his face. He says he can't say, so Agrias tells him he can't come along. When he begs, Ovelia overrules her guardian and allows him to come along. The party continues on towards the castle.