One Piece is currently in the Elbaph Arc, where the stakes are higher than ever with the introduction of the God’s Knights. Shamrock, the commander of this elite guard of Mary Geoise, is the twin brother of Shanks and is presumed to be one of the most formidable characters in the series.
While his limited screen time in the manga so far has yet to showcase the extent of his abilities, Shamrock’s fearsome potential was hinted at through his mastery in wielding his sword. Shamrock’s sword, Cerberus, is believed to be one of only two blades in the series that have “eaten” a Devil Fruit.
Earlier, fans had gotten acquainted with the concept of a sword with Devil Fruit powers through Funkfreed, Spandam’s weapon. While it was fascinating to watch, Funkfreed was far from dominant due to its users’ poor skills. Cerberus, on the other hand, has proven to be among the most dangerous swords in One Piece, primarily due to Shamrock’s talent.

While it has not been confirmed whether Cerberus has actually eaten a Devil Fruit, most fans hypothesize that it contains a Mythical Zoan-type Devil Fruit that represents the three-headed dog that guards the Underworld. In general, Cerberus only looks like a normal blade. However, when Shamrock activates it, the sword lets out black smoke to signify its awakening.
Soon after, a giant, monstrous dog with three heads appears, viciously wild yet obedient to the commands of its master. As mentioned, the weapon was first shown in the Elbaph Arc, when Shamrock and Gunko tried recruiting Loki to the God’s Knights to gain control over the Giants.
However, the Accursed Prince did not cooperate, even taunting Shamrock and angering him. To make the Giant pay, Shamrock activated his sword and ordered it to fatally harm him. Though Loki managed to survive, he still suffered grave injuries.
How powerful is Cerberus in One Piece?
While Cerberus cannot be classified under any specific grade of blades, it has proven to be among the most dangerous weapons in One Piece. So far, Shamrock has only displayed one technique with the blade, called Scramble, where the dog heads detach from the main body and obey the wielder’s orders.
The God’s Knight had used this to attack Loki, during which time a blade emerged from each head of the dog and pierced through the Giant’s body. This was a terrifying feat, as Loki is believed to be capable of destroying the world.

He is one of Elbaph’s strongest warriors, is immensely durable, and has a bounty of 2,600,000,00 berries. Loki has also notably clashed with Shanks in the past, and while the complete battle hasn't been revealed, it is believed to have been an intense confrontation.
Taking all this into consideration, it is highly impressive that Cerberus was able to make the Giant fear for his life and stab him so brutally. Combining this with Shamrock's ruthless personality, the sword is sure to give rise to more devastation as the story heads deeper into the Final Saga.