After revealing his true colors, he becomes the final antagonist in the series.
After eating a piece of Chaos, Cath grows in size, getting a long tail that ends in three points, white eyes, a big mouth with sharp misaligned fangs and a long tongue.
In his real form, Cath Palug is a gigantic feline creature with dotted patterns across his body. He has a long tail that ends in three points, a big mouth with fangs that go through his cheeks, big pointy ears, a long tongue and eight legs.
Not much is known about Cath's personality, as it has remained mostly silent other than sneezing at times. It prefers to stay on Arthur's head (and later his shoulder), and has refused to leave Arthur's side. Cath has the ability to talk, and has stated it is happy that Arthur is growing stronger. Cath appears to enjoy chewing on Arthur's hair and his cape.
However, when Arthur becomes the King of Chaos, Cath reveals his true colors as an evil, greedy and wild monster. He reveals that he remained by Arthur's side and protected him only to be able to devour him as soon as he awakened the power of Chaos so he could bring about mass destruction for no other reason than he could.
He is also sadistic, mocking Arthur about Camelot's destruction in the first fight between the Seven Deadly Sins and the Demon King and takes joy in the young king's despair and tells him that there is no point as everything, even the gods, eventually die and that even if the Sins and the Demon King hadn't destroyed Camelot, something else would've, so that he'll finally make Arthur lose hope and take all of Chaos from him.
Cath Palug was originally a creature born from the Mother of Chaos as the incarnation of the desire and obsession for power, to the point where it wished to become the King of Chaos itself. The tyrant beast challenged Chaos, but lost the fight and was banished. However, Cath Palug continued its misdeeds and was eventually sealed away by the Goddess Clan in Purgatory. It's unknown how it escaped from the seal or how Arthur managed to find it after training in Istar.
After Arthur and Gowther have completed their training and return to the group, Cath is on top of Arthur's head. Merlin asks Arthur what the strange object on top of his head is, and Arthur and Gowther merely reply that it is a mystery. 
After leaving Istar, Gowther tries to remove Cath from Arthur's head, but cannot do so and only ends up hurting Arthur. Gowther notes that Cath seems to be stuck to Arthur. 
Cath remains on Arthur's head throughout the Great Fight Festival.
Cath is still with Arthur when this, Nanashi and other Camelot knights fight against a horde of Gray Demons. When hearing it speak, Arthur is surprised and Nanashi affirms that Arthur would not die while Cath is with him. When the group is forced to retreat before the arrival of a Blue Demons horde, Cath agrees with Arthur that he must become stronger.
Cath, along with Arthur, is hidden in an underground shelter with the other survivors of Camelot. When Arthur arrives with Orlondi, Cath launches on this and keeps quiet about showing off.
Cath accompanies Arthur when he decides to go on his own to the castle of Camelot and recover the holy sword Excalibur. Being caught in the Marchen Maze of Peronia, Cath takes advantage when Arthur is attacked by a Gray Demon to approach Peronia from behind and devour her.
After entering the castle, Arthur and Cath are surprised by Zeldris and Cusack. Cath decides to give Arthur the possibility of running away by levitating several objects around and attacking the demons with them. However, Cath is defeated and seriously injured.
When Arthur is able to wield Excalibur, he gives several cuts to Cusack to retrieve Cath and take him out of the castle. Arthur apologizes to him for making him suffer, to which Cath tells him he is hungry and Arthur says they will eat when they are finished.
After Arthur failed to defeat the demons, Cath points out that his magical power is still not awake and that he will not win if it does not wake up. When Arthur suffers the effects of brandishing Excalibur, Cath sends a telepathic message to Merlin warning her that Arthur will die.
When Merlin manages to remove Cusack with her Icicle Castle, Cath is teleported with Arthur to the Boar Hat in Liones. Hawk is alarmed to see him hurt but Cath insists that they must worry about Arthur. However, Arthur falls victim to Cusack's Resonant, piercing his own heart with Excalibur. Cath looks horrified to see such a fact.
When Arthur dies, Hawk tries to comfort Cath, but it is intimidated by the monstrous expression of the cat.
Cath remains next to Arthur's body in the Boar Hat, until Merlin decides to carry out Arthur's awakening as the "King of Chaos". Seeing Arthur alive, Cath rejoices and jumps into his arms, but surprisingly tries to devour him. Meliodas manages to save Arthur, but Cath ends up ripping an arm and eating it, undergoing a monstrous transformation. The Lady of the Lake tells them that they must retrieve the arm or they will soon know how powerful even a fragment of Chaos can be.
After the Lady of the Lake reveals his true identity as the monster Cath Palug, Arthur asks Cath to stop since there must be a good reason for what he is doing since he protected him with his life. However, Cath Palug reveals that he only did so that Arthur could awaken as the King of Chaos, since he would not have had a good taste by devouring him otherwise. The monster then asks an affected Arthur if he can eat him now, creating a pocket dimension with the fragment of Chaos he had devoured and sucking Arthur as well as the Sins in it. There, Arthur asks him what he is for him, to which Cath Palug replies that he is food that he has been waiting patiently for and asks to let him eat without disturbance.
Arthur then destroys the dimension with a reincarnated Excalibur. Cath Palug is amazed and asks Arthur to let him eat every part of him. Arthur says that upon hearing that, he feels he can kill him without any regret. When Cath Palug throws himself at him, Arthur cuts him with Excalibur, apparently destroying his body in pieces.
Later, after Merlin sends Elizabeth, the Sins and Hawk back to Liones, she brings Arthur to rest inside one of the towers he unconsciously created but it is attacked when Cath appears, still alive and transformed further due to still possessing Arthur's arm within its body. Cath declares that he can smell Arthur inside and and asks him to go out and play again since he will not lose this time, only for Merlin to attack him and declaring herself to be its opponent.
After avoiding Merlin's many attacks, Cath surprises her from behind and gives her a slap, but Merlin teleports behind him and attacks him with a lightning bolt. Cath does not suffer any damage and responds with a ray of energy from her mouth. The monster claims that Merlin is not who he wants to play with. Arthur jumps there saying that he must be, since he must end Cath to amend his mistake of taking him with him.
Although Arthur cuts it back into pieces with Excalibur, Cath quickly regenerates himself saying he can't beat him that way. Arthur vows to defeat him no matter what, since it is his duty as king to protect his kingdom and his people from all those who threaten them. Cath then laughs saying he has already lost all that, revealing that Camelot was destroyed in the battle against the Demon King. Arthur is shocked by it, to which Cath tells him to use Chaos' power to confirm that his words are true.
As Arthur loses his will to the truth in spite of Merlin's words, Cath tries to crush him with his paw but soon withdraws it from the heat of the surrounding aura. Merlin attacks him again, but he dodges and knocks her down with a tail hit. Cath then releases a large bunch of beams from his mouth, but they are all reflected by Meliodas' Full Counter who arrives with the Sins and Elizabeth to help Merlin.
Cath Palug starts to regenerate stating that he is sick and tired of everyone always getting in his way. He then asks Arthur if he is really that shocked about losing his country and people, since all countries eventually fall, and that even if the Demon King and Sins had not done so, he himself, someone else, a meteor or perhaps the ocean itself would have destroyed it anyway. Arthur asks what he wants to reach, to which Cath Palug tells him that everything is the same. Arthur asks what he means and Cath Palug says he is warning him to give up fighting the inevitable given that regardless of the route taken, everyone eventually dies. Arthur asks if he should then just let him devour him and be fine with that, to which Cath Palug responds in the affirmative.
Ban and Meliodas interrupt pretending to start the fight by saying they have talked enough. Complaining about them being boring, Cath Palug encloses everyone within an illusion. Meliodas specifically dreams of Merlin suspending Cath Palug in time, then each departing on his own path, marrying Elizabeth himself only to see her die when she reaches old age before him. Cath Palug then attacks the kingdom and fights with Meliodas mocking that he is alone because in that chaotic world there are no constants and everyone finally leaves as if they had never been. However, the voices of his loved ones tell Meliodas that he will never be alone because their bonds will never break. This awakens Meliodas from the illusion, surprising Cath Palug.
Arthur and Meliodas still intend to defeat him, but Cath Palug says it's useless since they can't kill him. He declares that he will devour Arthur to unify with Chaos and devour everything. However, when Cath throws himself at them, Arthur says he discovered how to beat him.
Cath mocks his claim by asking if he plans to burn him, melt him, crush him, hit him into pieces or all of the above. He says he will devour him before he has the chance, invoking Chaos' power to open the dimension in his mouth. Arthur says that the only one to be devoured is Cath, and then invokes Chaos to create the same type of dimension with a mouth that begins to absorb Cath. Arthur says that if he can't defeat him then he will absorb it and at the same time recover the Chaos that he stole from him.
Cath Palug says that Chaos' power belongs to him and that as its direct offspring, he is the only one who deserves to have it. Arthur then asks him what he wants to do with that power to which Cath says he intends to destroy everything, leading Merlin to elucidate that Cath Palug is nothing more than a desire for destruction born of Chaos. Cath asks Arthur what he is planning, if he didn't learn his lesson, to create a new kingdom that will eventually succumb. Cath says that all his beloved subjects now hate him as the useless king who could not protect his people or his kingdom. Arthur says he does not want others to recognize him as a good king, but to create an everlasting kingdom in which everyone can be happy. Cath calls him stupid, saying that nothing is everlasting and that such a kingdom is a contradiction, to the point of it being Chaos. Cath is then silent when he becomes aware of what he admitted and as Arthur declares himself the King of Chaos, Cath Palug is completely absorbed.
After devouring Arthur's right arm, Cath absorbed a fragment of Chaos itself. With it, Cath was able to create a pocket dimension in his mouth that sucks his targets inside; or entrap them inside visions of their possible futures. He also obtained incredible regeneration abilities overcoming immortality, being able to rebuild his body even after being cut into pieces. Merlin goes so far to say that he becomes a being that transcends life and death itself.
In his gigantic form, Cath possesses incredible physical strength and endurance, being able to withstand Merlin's magical attacks without apparent injury. He is also very fast, being able to evade Merlin's attacks and attack her by surprise without her anticipating. In this form he can also launch energy attacks from his mouth.
Originally, Cath was a mysterious cat-like creature that found Arthur during his training in Istar and refused to let go of him no matter what and never said a word to him, until a month after Meliodas' death where he compliments Arthur on his fight against the Demons, saying he would like him to become stronger which shocks Arthur as he didn't know Cath could talk before then.
Since then, Cath has remained attached to Arthur's shoulder and only lets go when he's hungry and wants to feed, usually by eating anything or anyone he sees as "tasty", such as the demon Peronia. After infiltrating the castle of Camelot, Cath risks himself to buy Arthur time to get to the sword and shows intense rage over Arthur's death after Cusack uses his magic to run Excalibur through his heart.
After Merlin resurrects Arthur as the "King of Chaos", Cath appears very relieved at Arthur's return to the living world but immediately attempts to devour him and reveals the only reason he was near Arthur was to take the power of Chaos for himself after it awoke. Even going as far as to say he sees Arthur as nothing but food.
Right before his defeat, Cath shows extreme desperation to reject Arthur's power from taking back the fragment he took and mocks Arthur's claim at building an "everlasting kingdom", saying it is contradiction before realizing he fell into Arthur's trap as he is horrorfied to have lost the struggle and is promptly absorbed back into Chaos from wence it came.
King of Chaos arcEdit
- Arthur Pendragon vs. Cath: Lose
- Seven Deadly Sins & Arthur Pendragon vs. Cath Palug: Lose
- Cath's name is a direct reference to Cath Palug, a monstrous cat in Arthurian legends.
- Arthur named it Cath after the sneeze it made.
- It refers to itself in the first person as "Poku" presumably an old pronunciation of the first person, "Boku".
- According to the databook(s):
- Special ability: Not letting go of Arthur no matter what
- Charmpoint: His roundness
- According to his power level, Cath has the highest amount of Spirit measured accurately thus far in the series.
- Cath would beat Hawk in a fight.
- Cath is Welsh for cat.