Do note that this fight is only available whenever the Radahn festival isn't active. If it's currently active it can be deactivated by defeating Starscourge Radahn and talking to Castellan Jerren once more in the chapel just before the lift down to Radahn and then reloading the area, preferably by teleporting to the Chamber Outside the Plaza Site of Grace.
Notes
The innate, Unique Skill: Wave of Destruction is technically a ranged skill but in practice it's quite usable as a melee attack due to its Hyper Armor.
Has semi-unique one- and two-handed charged heavy attacks, where the usual attack is followed by a burst of stone chunks from the weapon's gravity magic.
Though both parts of each attack deals damage, they technically have the same amount of damage potential due to having a Colossal Sword's usual Motion Values divided across two attacks. In practice its damage will be slightly lower due to not being as able to overcome Defence.
Deals 50% more Stamina damage against guarding opponents than a Colossal Sword's charged heavy attack usually does.
These attacks award twice the amount of points towards the Winged Sword Insignias' damage buff due to both hits granting the usual 14 points each separately.
While this weapon scales with both Strength and Intelligence, it is borderline useless to actually invest in the latter anywhere beyond meeting the Attribute requirements. This is because the damage are incredibly minimal to both normal attacks (maxing out at +32 Magic Attack Power with 99 Intelligence if the weapon is upgraded to +10) and because unlike how these sort of weapons scale normally, where Intelligence provides minimal weapon Attack Power bonuses but great skill Attack Power bonuses, both weapon upgrade level and Strength provide far greater bonuses to the skill's Attack Power.
If the player meets the requirement for Strength but not for Intelligence, they will not be able to take advantage of Intelligence scaling, but the base damage of the Physical Attack Power will scale as normal, and the Magic Attack Power will not be reduced. This can ironically make it a good weapon for pure Strength builds as they effectively don't lose much damage but not meeting the Intelligence requirement.
Despite the appearance of its effects it does not cause bonus damage to gravity-type enemies (Fallingstar Beasts and such), presumably because it is not extraterrestrial in origin.
Increased physical block rate and guard boost of the Colossal Sword, Colossal Weapons, Great Sword, Great Hammer, Great Axe, Great Spear, and Halberd weapon classes.
The guard damage negations for the Ruins Greatsword went from 65/56/50/50/50/45 to 82/56/50/50/50/56.
Trivia
The ruin that the rubble used to make this sword originated from was most likely Crumbling Farum Azula, giving its dilapidated state and nearby location.
While the weapon resembles the Fume Ultra Greatsword from Dark Souls 2 (external link) and Dark Souls 3 (external link), it even more so resembles the King's Ultra Greatsword from Dark Souls 2 (external link) especially because of its resemblance to a statue wielded on a hilt.