Demon Mail

The Demon Mail is a cursed Armor-class piece of armor found in Golden Sun and Golden Sun: Dark Dawn. It give the strongest defensive boost in the original Golden Sun.

Basic Description by Game
The Demon Mail increases the wearer's base Defense by 50 points, but lowers the wearer's Jupiter resistance by 10 points. It is a Cursed Artifact, meaning that an Adept who has equipped it cannot remove it on their own; additionally, the Adept may occasionally be immobilized by the curse during battle. Demon Mail can be bought for 17000 coins and sold for 12750 coins.

In Golden Sun, the Demon Mail is found on the bottom floor of Crossbone Isle at the Pirate Ship, and it will materialize only if the player conquers the optional boss Deadbeard in a nearby battle. It can be equipped by Isaac and Garet, as well as Felix and Piers if transferred to Golden Sun: The Lost Age as part of a password-enhanced game. In Dark Dawn, the Demon Mail is found in this game's version of Crossbone Isle, a dungeon only accessible after defeating the final boss at least once. It can be equipped by Matthew, Tyrell, and Eoleo.

Analysis
Although it has the highest defensive rating in Golden Sun, it is not actually the best because of the decrease in Jupiter resistance. If the player chooses to have one character equipped with the Cleric's Ring, then they may choose to equip the Demon Mail in order to maximize the Cleric's Ring's effect. Otherwise they are better off sticking to the Dragon Scales or the Storm Gear.

In Dark Dawn, the Demon Mail will see even less use than it did in Golden Sun. It is not available until after the main storyline is complete, and requires the Cleric's Ring to negate its Curse. By this time, the player will have access to equally strong Armor, such as the Xylion Armor which has just as much defence and raises attack, that does not have the negative benefits of the Demon Mail.