Valkyria Revolution

This will pop after the second battle with General Viktor (the two headed robot snake) which I believe is the second or maybe third story battle of Chapter 10. His right head and one section below the head (left when facing him head on) is weak to physical attacks while his left head and one section below (right when facing him head on) is weak to fire magic. If you attack the wrong way it only does 1-2 damage so "weakness" is really the only way to do meaningful damage. The heads will bob around out of reach so rotate your attacks on whichever is close to the ground.

Both head parts must be broken for the battle to end. If you break one, after a short while it will regenerate health and the battle continues, so you want to wear them both down pretty evenly.

He has two grenade launcher body sections in the middle of the two heads. I don't think they are necessary to be broken to end the battle as I'm pretty sure at least one regenerated when I won. They are pretty easy to break though with physical attacks so I kept breaking them to cut down on the damage to my party.