Final Fantasy Tactics Walkthrough

Speed will be your best friend in this battle, as taking out the five Ultima Demons will be a big challenge unless your team is overleveled on balance to the enemy. Argath should get a turn fairly early and will approach the party to use some of Gaffgarion's skillset. If you want to take out the Ultima Demons, move with your entire team as a whole and start with the lone demon atop the wall where Argath started. This will keep you mostly out of range of the other demons at least for a turn or two. The demons are much slower than the primary opponent and you should be able to take out that one before it gets a turn.

Staying out of the range of the demons is key, so characters with guns - either the Ras Algethi (if you've done that sidequest already) or the Glacial Gun (hopefully stolen from Barich) - will be a big help here. Move your way around the perimeter of the map to keep out of range of all the demons at once.

If you're a lower level and/or simply don't want to deal with the demons, focus entirely on Argath. He has very high defense and will take limited damage from your attacks, but powerful characters like Orlandeau or Agrias will deal a lot of damage to him. Jumping on him, especially if you're using the Javelin II (also from sidequests), will also deal a lot of damage, as will a strong Samurai using the Muramasa, or a Ninja attacking from behind. You shouldn't have too much trouble here if you just unload your most powerful abilities on him right away. You can blow through this battle pretty quickly, but Argath and Ramza will banter quite a bit if the battle carries on, and that may be worth spreading things out more.

Once defeated, Argath fades away after calling out in despair for his mother. No need to see his like again.