Lachesis' Rule

A Lachesis' Rule is a Staff-class Artifact weapon found in Golden Sun: The Lost Age and Golden Sun: Dark Dawn. It has the highest attack rating of all Staff-class weapons.

Basic Description by Game
In all its appearances, Lachesis' Rule increases the wielder's attack by 177. It can be sold for 16275 coins and subsequently re-bought for 21700 coins.

In The Lost Age, it is dropped by Mad Demons in Anemos Sanctum, although the odds of receiving it are very slim. Being a Staff, it can be equipped by Jenna, Ivan, Sheba, and Mia. Lachesis' Rule's Unleash effect is Apocalypse, which activates at a rate of 40% (notable, since most Unleashes activate at a rate of 35%). It converts all damage to Jupiter damage and attacks with an additional 125 attack points, which is higher than any other Unleash in the game (though it still pales in comparison to the damage multipliers of some of the game’s strongest weapons, like the Sol Blade and Excalibur). In addition, it sometimes curses the target, automatically killing them after approximately 7 turns.

In Dark Dawn, Lachesis' Rule is once again a rare drop. The Red Wyvern in Crossbone Isle drops the Lachesis' Rule at a rate of 1/128. The rate will increase to 1/32 if an offensive Jupiter Djinni is used to fell the Red Wyvern. It retains Apocalypse as its main Unleash but gains three new unleashes: Critical Move, Double Attack, and Spiral Assault. Critical Move is a non-elemental physical attack that multiplies damage by 1.4. Double Attack is a Jupiter-based Unleash that multiplies damage by 1.6. Spiral Assault is a Jupiter-based Unleash that multiplies damage by 1.3 and has a range of 3 targets.

In The Lost Age
Although powerful, Lachesis' Rule may not see much practical use seeing as it is acquired so late into the game. Anemos Sanctum can only be entered once the player has collected all 72 Djinn, making it the  final (although optional) dungeon in the game. This makes the already risky Curse inflicted by Apocalypse rather trivial: by this point the  party should be strong enough to defeat most enemies before the Curse  could complete its work. Also, although unlikely, Jenna and Ivan may have already acquired the stronger Tisiphone Edge, capable of  doubling or even tripling the damage done. If this happens, the only Adepts who would need this weapon are Sheba and Mia.

Atropos' Rod vs. Lachesis' Rule
At first glance, it seems that Lachesis' Rule is the game's most powerful Staff,  with Atropos' Rod coming in at a close second. However, upon closer inspection, it's possible to say that Atropos' Rod is the  stronger of the two. The most obvious reason for this reversal of power is in their Unleashes: Atropos' Rod's Unleash, Life Shear, has a  small chance of instantly killing the target, which is a huge advantage  over the time-consuming Curse caused by Lachesis' Rule's Unleash,  Apocalypse.

Also to be taken into consideration is when these two items can be obtained. Lachesis' Rule can only be found in Anemos Sanctum, which can't be entered without all 72 Djinn. This requires the player to collect all 28 Djinn in Golden Sun, transfer  their data to Golden Sun: The Lost Age, and then locate the remaining 44  Djinn. Because of this, some players may not even reach Anemos Sanctum, let alone get a Lachesis' Rule. In comparison, Atropos' Rod is fairly easy to obtain, requiring little more than access to the interior of the  Yampi Desert Cave.

This isn't to say that Lachesis' Rule doesn't have it's advantages over  Atropos' Rod. The most notable advantage is that Lachesis' Rule has a higher attack rating, which can make a huge difference since the  characters that can equip these weapons usually have low attack ratings. Also to be taken into consideration is the elements of their Unleashes. Life Shear is of the Mars element, while Apocalypse does Jupiter damage. This makes Atropos' Rod an excellent choice for Jenna, whose high Mars power would make Life Shear even stronger, while the same idea  makes Lachesis' Rule ideal for Ivan and Sheba. However, Jenna and Ivan may find the attack multiplier of the Tisiphone Edge to be stronger  than either of the Staffs (although it is worth mentioning that their  Venus power does have an impact on the damage dealt), leaving only  Sheba to take full advantage of the Unleashes.

In the end, which Staff is stronger is largely a matter of personal preference.

In Dark Dawn
In Dark Dawn, Lachesis' Rule may not see much use, since it can only be acquired after the main game is complete. Additionally, the lack of RNG manipulation methods means that acquiring Lachesis' Rule is a matter of luck.

Lachesis' Rule, like many "ultimate weapons", has had its consistency reduced due to the increase in Unleashes. Since Unleashes are now chosen at random from four, this means that Apocalypse has a much smaller chance at activating. While Double Attack is fairly solid, Critical Move and Spiral Assault are comparatively weak. Thus, there is less of a guarantee for inflicting large amounts of damage.

To this extent, Atropos' Rod seems to have overtaken Lachesis' Rule. It is available before the final battle is fought, though still as a rare drop. Additionally, it only chooses from one of three Unleashes; thus Life Shear will activate more often than Apocalypse. Finally, Life Shear now has a chance to automatically kill anyone within a range of three targets, which helps to compensate for its smaller chance of activation compared to The Lost Age.

RNG Method (The Lost Age)
Like many weapons that are rare drops, certain methods can be used to ensure that Lachesis' Rule is a guaranteed drop. These methods generally involve manipulating the Random Number Generator through specific battle strategies. One method for acquiring Lachesis' Rule is listed below. Enter the Anemos Sanctum (requires all 72 Djinn). Save game. Reset. Wait until you encounter a Mad Demon accompanied with something.

1st Round (big arrow on Mad Demon):
 * Felix casts Mother Gaia
 * Jenna casts Aura
 * Sheba casts Tempest
 * Ivan casts Tempest

2nd Round:
 * Felix attacks other monster
 * Jenna copies
 * Sheba unleashes Whorl (Mad Demon)
 * Ivan casts Plasma (big arrow on Mad Demon)

Cultural references
In Greek mythology, Lachesis is one of the three Fates. Lachesis was the weaver; she and her sisters appear within three days of a baby's birth to decide their fate. Lachesis measures the thread that is woven by Clotho, and decides the destiny of the being.

Each of the Fates has a weapon named after it in The Lost Age: Clotho's Distaff, Lachesis' Rule, and Atropos' Rod.

Trivia

 * The Lachesis' Rule is the only staff that has four unleashes. This is quite unusual since only the stronger bladed weapons have four unleashes. No bows or claws have up to four unleashes.