The Dark Judges have a philosophy that boils down to this. Undead psychopaths devoted to Law, they figure that since only the living commit crimes, life itself should be made a crime that is punishable by death. They slaughtered the entire population of their world, then found themselves stuck, as they hadn't any form of space travel, making them come off more as Kill All Humans in practice. They've killed the occasional alien traveler who made the mistake of visiting their world, though. It wasn't until one of those aliens brought a dimension-jump device that they started traveling to parallel worlds that they found teeming with life.
Sabbat the Necromancer from the Judgment Day arc is a powerful sorcerer who has made it his mission to destroy all life so he can use the corpses of the dead as part of his undead army.
Black Science introduces the draln, a cult of telepathic millipedes dedicated to ending suffering by ending the existence of life capable of suffering. They're nasty but contained on their homeworld - until they achieve interdimensional travel.
Clive Barker's Next Testament: Wick attempts to annihilate humanity after he sees nothing on Earth that is worth saving to his mind.
Jarek from Dinocorps, who strongly believes that anyone who isn't a Sauron like him deserves death. He blows up the world to kill off a race of dinosaurs, and then attempts to do it a second time in order to kill off all the humans.
The Ogdru Jahad from Hellboy want to burn the Earth to cinders, because they are the collective Beasts of the Apocalypse and thus feel they Must.
Grimjack: John "Grimjack" Gaunt walks away from Heaven to save his friends. The consequences were that he was denied any afterlife and was doomed to be reborn remembering his memories for all eternity. His soul was bound to the pan dimensional city known as Cynosure. Cynosure was build to harvest the energies of the multiverse to an entombed supreme being called Dis (firstborn of the multiverse) until it was ready to repeat the birthing process in an unending cycle. Grimjack's latest incarnation travels back in time to warn himself of the doom and to break it he has to end the multiverse by destroying Cynosure. Future Grimjack succeeds in manipulating present John in freeing the Supreme being from his sleep. In Grimjack's second incarnation we see the Supreme being walking around in mortal form giving the demons the chance to end his life and let the multiverse die in entropy. They fail. A huge hint that the multiverse might end up destroyed can be seen in Grimjack's supposedly real father, his uncle Jack. He is a Fey and can look into the future. He describes to a young grimjack the complete dissolution of the multiverse, saying there will be "nothing" after that and also that Grimjack's death would be the most interesting of all. We never see if future Grimjack succeeds because the series ended with the death of the second incarnation.
Ujo Dasa is a dark sorcerer from the Frazettaverse. He planned to free the Oblivion God "Mirahan" by sacrificing a half-breed human/demon and begin the end of everything. When confronted by his former teacher Dreovid, he says it's better to have "cool darkness than searing light". In the end it was revealed that Ujo was the half-breed and son of Mirahan. The Oblivion God swapped his throne of netherhell with Ujo and we watch him rest in peace.
Johnny the Homicidal Maniac implies in the former half of the series that Johnny may be at the center of the universe and that if he dies, all will cease to exist. This turns out to be true when a robotic arm with a gun he created shoots him in the head. As he slowly bleeds out, a Lovecraftian monster breaks free from his walls and destroys everything. Outside his home reveals to be an endless void. This becomes an Averted Trope when Satan brings him back to life thus reseting the world to its former self.
In DC's take on Masters of the Universe, Skeletor becomes this during the climax of "The Eternity War": Having defeated Hordak and seized control of the power of Greyskull from him — and having previously discovered that throughout The Multiverse, he always loses to He-Man — he intends to use his new status as a Physical God to cheat the odds by killing everyone and everything, so that he can then rule over a universe of the dead unopposed.
Lord Drakkon of Mighty Morphin' Power Rangers: Shattered Grid descends into this. After murdering the main universe Tommy Oliver and causing the Ranger timeline to shatter into multiple universes, he proceeds to go on a rampage through the universes in order to gain enough power to hop into the realm of the Morphin Masters, steal one of their hearts and obliterate the multiverse to rebuild it in his image.
The Mad Angel Apolyon from the Chaos!Multiverse stole secret knowledge from God and uncovered the truth that nothing really matters. Lucifer fearing this truth imprisoned and tortured Apolyon for a thousand years. After he was released God confided in him that for Heaven to exist, there must be a Hell. Apolyon betrays God and wants to destroy all of creation beginning with Hell. Without its counterpart, Heaven will fall and in turn so will God. In the end as Apolyon said, there will be nothing!
Dr. Finitevus firmly believes that the world is corrupt and needs to be "purified in emerald fire". This is why he manipulated Knuckles into becoming the new Enerjak, knowing that the power would drive him crazy and lead to him going on a rampage. He hasn't tried anything major since, but he's still convinced of the righteousness of his actions and there were hints that he had big plans before he was Exiled from Continuityby the lawyers.
The only character who manages to be even more omnicidal than Zachary is Sonic's Superpowered Evil Side, Super Sonic, who has no real plan beyond destroying everything in the vicinity when Sonic transforms.
After a Villainous Breakdown, Dr. Robotnik gives up trying to rule Mobius and tries to destroy it outright.
Master Darque from the new Valiant Universe. After destroying countless worlds he is coming for Earth. He wants to use the souls in Deadside to break down the barriers between worlds and kill every living being. Using all the souls to become a God: "Every creature on this world raises its head against a background of infinite carnage and smiles at the sun and declares the world good. We are all monsters. Because the Universe we live in is monstrous. But we are blind to it. We do not see the endless horror that underpins our lives. Because God is a sadist. The perversity of this reality is undeniable proof of both his existence and his malice. And it is our duty to become his superior. I will find him. I will challenge him. I will free us. I will make him pay for what he has done. I will break the wheel. I will end all suffering. And you would stop this?". Darque only wants Godhood so he can erase all of existence and bring blessed Oblivion to everything, himself included.
Deadside in the old Valiant Universe was a terrible place where all souls eventually come no matter how they lived be it good or evil. There is no Heaven nor Hell. Billions upon billions of souls trapped for all eternity screaming in madness. In the new Valiant Universe, it seems to be toned down a bit, but it's still a terrible place where lost souls find no peace. Darque also comments on the nature of souls and its curse: "Even the smallest of them. There is something in all of use that persists beyond death. You would call this a soul. The essence of a thing that is indestructible. Something that survives. Something that fears. Something that suffers. This is cruelty. This is madness. To know that your suffering will never end. Because that is the point of the soul. Suffering without limit. Without Surcease."
Pain, the servant of Desire schemed to end the world/reality/time by manipulating Adam Case. He was not alone as he was backed by a group of mythological powers:
Coatlicue, the Aztec earth mother goddess suffers immensely because of the pollution of the earth. The only way to stop the poison coursing through her veins is to destroy the world and she would gladly give her life for that purpose.
Tezcatlipoca, the Aztec god of night and confusion,betrayal,divination,etc...grew tired of life and decided to team up with Pain to obtain his one way to ticket to that "permanent vacation". He changes his mind at the end of the series when he has found fun in screwing with people on "a personal level". His lover "Leatherette" follows suit and betrays Pain .
Leatherette, a demon who works directly under Pain and shares Tezcatlipoca's reason for ending the world. The two eventually find purpose in raising hell on earth and betray Pain.
Tantalus was cursed by having immense desire and never be able to fulfill it. He was betrayed at the last battle and found momentary peace at the hands of Enna when he shot him up with heroin.
Enna, an old Babylonian Plague God has adapted to the modern times and delivers plagues of pharmecuetical origin like heroin. Only when he has dipped into his own pharmacuetical supply does he refuse to help Pain end time. His new plan is to destroy Pain but is stopped by Desire herself.
