Zak Monday is near identical to his positive universe counter part with the exception of his hair being primarily white with the top being black. He is a young man of slender frame and has a tan complexion.
Zak Monday is an individual who takes pride in being evil and causing mayhem whenever he can while also looking down on everyone including his own family with the exception being Komodo Monday who he shows some minor respect for. While he is somewhat skilled in fighting he often lets his pride get the best of him due to feeling he is superior to even his positive counterpart which has led to his defeat.
Zak Monday first appears in "Black Monday", he and his fight the Saturdays but are defeated and sent back to their world. However, he & Komodo Monday were able to escape the mirror while ignoring the pleas of their family to start their own rampage.
Zak makes his second appearance in "Paris is Melting" where he and Komodo Monday are going on a rampage in Paris. The pair kidnap Zak, Fiskerton, Komodo and Zon. They also try to put their positive counterparts in their world given the dangers of both the versions existing in the same dimension when near each other. He and Komodo were later tricked by Zak and sent back to their world, where they are beaten up by their family for leaving them.
In "Your Enemies Closer", Argost reveals he found about Zak Monday and sees his powers as more useful than his counterparts. Zak Monday is released by him to steal his powers. On sight, Zak Monday attacks his counterpart. However, Zak tries to warn him that Argost only wants his powers, though Zak Monday does not believe him and calls him crazy until Munya traps him in webbing. Argost then admits to the trapped Zak Monday that he will steal his powers. Argost using Devonian annelids and the flute of Gilgamesh to steal the screaming Zak Monday's abilities, killing him in the process.
Zak Monday has similar powers to his positive counterpart but instead of merely being able to influence cryptids he can control them and drive them violently insane while doing so. Given Anti-Kur has all the powers of Kur who has been stated that those who could gain control of Kur that they would have limitless power over cryptids and gain eternal life, due to this and how Kur was ancient before his first defeat it is implied both Zak's have either extreme longevity if not outright a form of immortality. Much like his positive counterpart it is also shown to have enhanced strength and reflexes though his arrogance tends to get the better of him.
Given how all the character are the opposite of how they are in the main world many assume the Anti-Kur would be a benevolent god while the normal Kur is considered a malevolent god who is said to one day destroy humanity.