Phantasmal Mail

The Phantasmal Mail is an Armor-class piece of armor found in Golden Sun: The Lost Age.

Basic Description
The Phantasmal Mail increases base Defense by 38 and base Luck by 7. In addition, it can be Used as an item by an Adept that has it in his inventory and is able to equip it (but it does not actually have to be equipped) to emulate the Delude Psynergy to attempt to inflict Delusion on up to three enemies in battle. It can be bought for 5800 coins and sold for 4350 coins, if sold while broken the resale value drops to 2900, and it can be repaired by a Vendor for 1450.

It is found in a treasure chest in Izumo Ruins, a dungeon which requires the Sand and Parch Psynergy to explore properly. As an Armor-class item, it is equippable by the warrior-style Adepts Felix, Piers, Isaac, and Garet.

Analysis
The Phantasmal Mail is sure to be an upgrade to at least one of your two warrior Adepts' defense, even if they are both equipped with Plate Mails, and the substantial Luck boost will help lower the frequency of that Adept being afflicted by a negative status condition. It is likely to stay on for at least a while, until Lemuria is reached. Its Use effect is an entirely incidental bonus in light of this.