Claymore

A Claymore ("Bastard Sword" in the Japanese version) is a common Long Sword-class weapon available throughout the  Golden Sun series.

Basic Description by Game
In all appearances, a Claymore increases the wielder's base Attack rating by 70 points. As a common item, it can be bought repeated from Vendors for 4000 coins each and sold for 3000 coins each.

In Golden Sun, Claymores are sold in the towns Altin and Kalay, and can be equipped by Isaac and Garet. In Golden Sun: The Lost Age, Claymores are sold in the towns Kibombo and Yallam, and can be equipped by Felix and Piers.

In Golden Sun: Dark Dawn, Claymores are sold in Te Rya, Belinsk, and Saha, and can be equipped by Matthew and Tyrell. Due to changes to the Unleash system, Claymores now have two Unleashes: Critical Strike and Spin Strike. Critical Strike is a non-elemental physical attack that does 1.5 times the damage of a normal attack, while Spin Strike is a Jupiter-based Unleash that hits three adjacent targets.

Analysis
In Golden Sun, Claymores are the strongest common weapon in the shops at Altin, but at Kalay it will be overtaken by the Great Axe at 5200 coins. The weapon shop in Altin will be open once the town has been un-flooded, and a Claymore is a worthy purchase to replace either a Broad Axe or the Arctic Blade if they're held by the two warrior Adepts in your party by then. With a price tag of 4000, it is only really sound to buy one Claymore, especially considering that in the upcoming Lamakan Desert dungeon-style location is a strong Mars-based axe artifact called the Vulcan Axe. After Altin, the Claymore will likely remain in your party's inventory until by the time you reach Tolbi.

In The Lost Age, much of the game's focus is on completing puzzles in the dungeon-style locations that provide as rewards weapon artifacts far superior to commonly bought weapons and even weapon artifacts that can normally be bought in vendors, so you should not buy and equip this weapon because it will most likely be overpowered by the equipment you already have (the Disk Axe, for example).

In Dark Dawn, as in The Lost Age, the player will be able to find superior Artifact weapons before they can buy the Claymore. Thus, the Claymore can be safely passed over. Before entering Te Rya, Tyrell will have the stronger Vulcan Axe, while Matthew can equip the Grievous Mace.