The Polter Armor is an enemy found in Fort Magrad. It is a suit of armor, along with a Polter Helm and Polter Sword that is seemingly possessed by the souls of humans that died in the Dragon Campaign.
This boss is optional, located on a path out of the way in Fort Magrad.
Hit Points: 3800
Hit Points: 2400
Hit Points: 2800
In this fight, Miranda equipped with a Darkness Stone will be a very powerful character indeed. The Armor throws countless Darkness-based magical attacks, which she will be able to combat very well being equipped with this Accessory. Also, her high magic attack combined with her Light-based Dragoon magic is incredibly powerful as well.
That being said, choose your characters wisely for this battle. It has a high magic attack, and throws many Darkness-based Attack Items.
As for which piece of armor to destroy first, the choice is based heavily on your biggest pet peeves in this game. The Helm has a habit of blocking a character's battle choices and/or causing status ailments; the armor throws an endless number of magic attacks, which can heavily damage your players without any time to heal them; and the sword can use a Can't Combat attack, which can be opposed with a Talisman. The sword, whenever it is destroyed, always uses this technique; it would probably be better not to save the sword for last.
Other than that, this battle is mostly attack with Light-based attacks or heavy physical attacks, and heal as often as possible.