Darksword

A Darksword is a Cursed Artifact Long Sword-class weapon available in Golden Sun: The Lost Age and Golden Sun: Dark Dawn. It is forged from a Dark Matter, and it has the highest base attack rating of any weapon in the series.

Basic description by game
The Darksword increases its wielder's base Attack by 210 points, which is the highest attack rating increase of any piece of equipment in The Lost Age - even higher than the Sol Blade, which has 200 attack. In The Lost Age, it is an Artifact weapon that is only acquired by bringing a Dark Matter forgeable material to the blacksmith in Yallam so that it may be turned either this or one of several other items chosen at random, with the chance for the Darksword being forged being 10%, and you must pay its 24200 buy value in order to obtain it. Afterward, it can be sold for 18150 coins, and can subsequently be bought back for 24200 coins. As a Long Sword, this can be equipped by Felix, Piers, Isaac, and Garet. It is a cursed item, which means that if an Adept equips it, he is inflicted with an equipment curse which causes him to be physically unable to de-equip it without assistance from a healer at a Sanctum. Also, if he is not equipped with the Cleric's Ring, then when in battle there is a chance he may be immobilized, unable to do anything whenever he attempts a battle command.

Its Unleash effect, Acheron's Grief, deals a Venus-aligned attack equal to the user's normal physical attack with 76 damage points added to the results, and there is a chance that it will inflict the target with the Venom status condition. Visually, Acheron's Grief resembles the wielder summoning a colossal purple-hilted sword that crashes down into the area where the target is, letting loose a water spout of purplish-blue energy as it digs into the ground where the target is, and detonating in a large explosion of dark energy as the screen temporarily inverts its color. It essentially resembles a purple-colored Titan Blade.

In Dark Dawn, the Darksword is obtained in much the same way, where you must bring a Dark Matter to Obaba at Champa and hope she forges it into this, though like all other equipment she forges she will give it to you for free. It and its Acheron's Grief unleash has all the same statistics and Cursed nature, and is equippable only by Matthew and Tyrell. With the different Unleash mechanics, Acheron's Grief is now the fourth and final Unleash that the wielder may gain the ability to randomly choose from whenever he unleashes. Its first Unleash is Mortal Danger, the main unleash of the Assassin's Blade from much earlier in the game, which deals a Venus-aligned attack equal to the user's normal physical attack with 28 added damage and the chance to instantly fell the target; its second Unleash is Spiral Assault, which is a Jupiter-aligned attack equal to the user's normal physical attack with the result multiplied by 1.3, and hits each adjacent foe so that up to three foes may be hit; and its third Unleash is Sky Diver, which is a Jupiter-aligned attack equal to the user's normal physical attack with 66 added damage and the chance to inflict the Stun status condition.

The Lost Age
In The Lost Age, a Darksword is certainly not a weak weapon, though the only way it can be made useful is if the Cleric's Ring from the original Golden Sun is transferred into The Lost Age by a Password data transfer, preventing the equipped user from occasionally not doing anything in a given turn. The highest base attack rating of all weapons in the game means that whenever the user deals a physical attack without Unleashing, the user will deal more damage then if he strikes with any other weapon without Unleashing. However, the Unleash is the most defining aspect of any weapon, and it is in this area that the Darksword seems quite average in comparison to other late-game weapons.

Acheron's Grief has both the highest added damage bonus of any unleash that an attacking "Warrior"-style Adept may trigger (the Atropos' Rod and Lachesis' Rule that "Mage"-style Adepts may Unleash with have higher added damage values) and a chance to inflict a good status ailment, Venom, which automatically deals potentially large amounts of damage to an enemy at the end of each turn. Despite this being a solid Unleash, the Darksword is nonetheless outclassed by the weapons with unleashes that multiply the damage they deal - the Sol Blade and Excalibur Long Swords and the Tisiphone Edge and Masamune Light Blades. You can only find one each of Sol Blade and Masamune, however, and an Excalibur is forged from an Orihalcon with half the probability that a Darksword is forged from a Dark Matter, while a Tisiphone Edge is extremely rarely dropped. This means that if you end up with a Darksword and a Cleric's Ring by the end of the game without some of the other aforementioned weapons, a Darksword is still a very good weapon for one of your warriors to wield.

Dark Dawn
In Dark Dawn, although all four of the aforementioned weapons also make return appearances in the game, the Darksword is no longer entirely outclassed by them. The redesigned Unleash system modifies the usability of essentially all the weapons in the game, for better or worse depending on the individual weapon, by adding several additional Unleashes that the game randomly chooses from each time the user makes an Unleash with that weapon. The four aforementioned "ultimate" weapons all become less consistently powerful because of this, but even so, the Darksword is also made more average by having three unleashes that are less powerful than Acheron's Grief.

However, the benefit to the Darksword is the resulting decreased practicality of Unleashes as a whole. The Sol Blade still can get high damage on average with its Unleashes, but it can only be used by Matthew in Dark Dawn, whereas Tyrell is left to use other weapons. Tyrell's best option for getting Unleashes with a high damage multiplier is Levatine, which has been improved to be one of the game's best Unleashes, but even when an Unleash is triggered, the average damage multiplier is only x1.6. In comparison, the Master and Ronin classes have Psynergy capable of consistently multiplying damage done by x1.5 and x1.8, respectively. As a result, it may be preferred to use classes like these and their powerful Psynergy rather than relying on regular attacks and the hope of a powerful Unleash. When using such a strategy, the Darksword's weak Unleashes cease to matter, and it becomes the best weapon for such a strategy due to having the highest Attack bonus of all weapons. Tyrell is the only Adept likely to take advantage of this, though.

The two things that cause problems for this are the curse and the late availability of the weapon. Like before, the Darksword can only be obtained by forging Dark Matter, but in Dark Dawn, this material can only be obtained in the Dark Dawn version of Crossbone Isle, an area that can only normally be accessed in the postgame after the final boss is first defeated. This can be bypassed through the Endless Wall glitch, but even by that means, the area cannot be reached until the Endless Wall itself can be reached, which is already close to the end of the game. The curse is also an issue, since the character equipping the Darksword must still hold the Cleric's Ring to be effective. Obtaining the Cleric's Ring is less of an issue than in the previous game, though, as it, like all of the Dark Matter, is found in Crossbone Isle. The only real problem with the curse is that it takes the same Cleric's Ring away from the other characters, but cursed items are still in low demand, so it also isn't much of an issue. This means that it is easy to make a Darksword usable at the end of the game, but you will need to use a glitch in order to use the weapon against the final bosses the first time through. The glitch is not without its costs, as leaving Crossbone Isle when accessed early and returning to the rest of the game requires dying to return to the Tonfon Sanctum, which forfeits half of your gold. So if you are unwilling to use the glitch for that or any other reason, the Darksword will be less useful, in a sense.

The first Unleash the Darksword may now trigger, Mortal Danger, is arguably a weak effect from an endgame perspective, because it adds a small amount of Venus-aligned damage while only occasionally triggering its instant-death effect on the non-boss enemy it is being used on. Spiral Assault is the only unleash with a multiplier and also the only unleash that hits multiple foes, and while this can occasionally be useful, the small multiplier of 1.3 often means that even the other added damage unleashes of Sky Diver and Acheron's Grief will do more damage to a single target in the end. Spiral Assault is also aligned with Jupiter, which is not an easy element to increase in power on the Venus and Mars Adepts that can equip this weapon, and so is Sky Diver, which is a single-target Unleash that otherwise adds about as much damage as Acheron's Grief. Sky Diver is not necessarily a bad unleash because of how it is close to the added damage strength of Acheron's Grief and can also trigger a somewhat useful status effect. But overall, the Darksword's Unleash collection noticeably lacks an effect with a high damage multiplier, which many other weapons have - even weapons that aren't "ultimate", like Levatine - which means that the Darksword wielder won't be scoring any large bursts of damage even occasionally.

Cultural References
In Greek Myth, the river Acheron ("stream of woe") was believed to be a branch of the underworld river Styx over which Charon ferried the newly dead souls across into Hades.