Apocalypse How/Class Z

""Every atom in existence is bound by an electrical field. The Reality Bomb cancels it out, structure falls apart...Full transmission will dissolve every form of matter...Across the entire universe, never stopping, never faltering, never fading. People and planets and stars will become dust. And the dust will become atoms and the atoms will become... nothing. And the wavelength will continue, breaking through the rift at the heart of the Medusa Cascade into every dimension, every parallel, every single corner of CREATION! This is my ultimate victory Doctor! THE DESTRUCTION! OF REALITY! ITSELF!!!""

- Davros succinctly explains what his Reality Bomb does, Doctor Who, "Journey's End"

Omniversal-scale Annihilation. Can take on two forms:

The Ultimate End Of All Things: The Physical Annihilation of everything, everywhere. Period. Only counts for fictional universes that have alternate dimensions or some such that would prevent Universal Physical Annihilation from working.

Cosmic Do-Over: The Metaphysical Annihilation of everything. It is not "the end of all things", because "after" this happens, nothing ever existed. There never was anything to annihilate; you can't have an end to something if you wipe out its beginning. This is the retroactive destruction of all of everything, everywhere.

Depending on whether the work treats Meta Fiction as a type of alternate universe, this may not be a credible threat since the destruction of all things would have include our own reality. There may also be Fridge Logic if it's likely that an alternate universe exists where the heroes failed to prevent the apocalypse. Both of these issues can be Justified or Lampshaded.

Anime and Manga

 * In Dragon Ball GT it's stated that Omega Shenron could have caused this.
 * Back on Dragonball Z anime. Majin Buu flew into a rage and his power began to tear the fabric of reality. Then, Vegeto stopped him by slugging him. Make that what you will.
 * In Soul Eater goes mad and decides at one point that the only way to  is to destroy all of existence. Luckily for everyone,  He's back to normal now.
 * Near the end of Futari wa Pretty Cure, the Dark King is purportedly destroying multiple planets in his spare time. His goal, as stated throughout the series, is the total destruction of all existence.

Comicbooks

 * In Grant Morrison's Doom Patrol, this is what will happen if the Anti-God, let free by the Cult of the Unwritten Book, is able to proceed with unmaking the universe. "Nothing. Forever and ever."
 * In Lucifer, the spin-off from The Sandman, all of Creation was nearly unmade when

Films -- Live-Action

 * In Dogma, if the Word of God is to be proven wrong all of creation will cease to exist.
 * This is the goal of the Warlock, and he comes Damned close.

Literature

 * All of Spider Robinson's time-travel stories are fueled by the premise that a genuine temporal paradox will result in the complete annihilation of space-time from beginning to end, not only destroying everything, but causing it never to have existed at all.
 * In "The Keys to The Kingdom" series by Garth Nix, if the House is destroyed by Nothing, reality will cease to exist (including all the Secondary Realms).
 * It's hinted that Suzumiya Haruhi has the power to do this (but not the mental sickness required to, at least not yet).

Live-Action TV

 * Unsurprisingly, Doctor Who has a few examples of this extreme:
 * In the finale of the 2008 series, Davros comes within a hair's breadth of destroying all matter in the entire multiverse save for himself and his group of Daleks.
 * The  attempt this or Class X-4 to 5 in The End of Time,.
 * The
 * The . This is soon approaching a Z-2.
 * It should be noted that Doctor Who has an example in every category for this trope. If there's one thing these people know, it is how to kill a lot of people/planets/etc.
 * In The Big Bang it reaches Class Z-3 - all realities never existed. Creation never existed. Nothing ever existed. The above statements ignore Earth and the moon and sun.
 * Note it's easy to miss that it's a Z-3 and not a Z-2, since its status is only confirmed in a single, blink and you miss it line of dialogue from a  in the previous episode. "All universes will be deleted."
 * It should be noted that only Doctor Who ever produced examples which can even remotely qualify for above vanilla Class Z.

Music

 * Actually happens in Food for The Gods. Satan leads an army of the damned into Heaven, and starts utterly laying waste to everything in sight. God responds by going completely insane with rage and obliterating all of creation.

Tabletop Games

 * This is the fate of Creation if the Nobilis lose their Valde Bellum. Retroactively, no less.
 * The Abyssal Exalted were created by the Neverborn with the express intent of throwing Creation into Oblivion, freeing the Neverborn from their fetters to existence by getting rid of existence.
 * This is the presumed goal of the Wyrm in Werewolf: The Apocalypse, although some speculate that It's goal is actually to make things as horrible as possible and keep it that way forever.

Videogames

 * The fourth or fifth endings of Drakengard if not for the intervention of the heroes.
 * The second Tasty Planet game has the Goo devour progressively bigger things, eventually getting to planets, stars, entire galaxies, and eventually the fabric of space-time itself.
 * Sonic the Hedgehog 2006 comes dangerously close to
 * In Sonic Generations, Time Eater wants to destroy time from at least 1991, resulting as if nothing ever existed, over what is certainly a personal grudge against Sonic. The game is set during this process of complete time-erasure.
 * Live a Live.
 * In Final Fantasy IX, Kuja comes within a hairs breadth of pulling one of these off.
 * In Final Fantasy VI, Kefka manages to succeed in a severe Class 1 destruction of the world, and when he learns to his disgust about people's hopes, love, and dreams, he decides that he'll "Destroy everything and create a monument to Non-existence."
 * In Dissidia the Cloud of Darkness and Exdeath had a talk about the differences in their plans to destroy existence. Exdeath himself may have rather ruled over everything but the Void has other plans.
 * The bad ending of the Demon path in Soul Nomad
 * In Super Paper Mario,
 * In Ratchet and Clank: A Crack in Time, this is implied to happen if someone tries to use The Great Clock for time travel.
 * Shin Megami Tensei Nocturne. True Demon Path.
 * In Chrono Cross,.

Webcomics
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 * In Homestuck, messing around with the fourth wall is supposed to be even worse than class Z, according to Karkat:

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 * It's true from the author's end too.
 * It's eventually revealed something is killing the Horrorterrors. According to Rose, this threatens the perpetuation of reality itself.
 * The threat of such an event is a major plot point in The Order of the Stick, in that.

Web Originals

 * In The Book of Stories OCT, the worst outcome of the Book's Unwriting could be classified as Class X-5 or even Z, though it's not as much destroying as it is making everything nonexistent.
 * In the game Ge Ne Sis, it's revealed that

Western Animation

 * In Transformers, this is Unicron's ultimate goal. Given that his overall method is to eat the entire multiverse one planet at a time, its taking him quite a while, but, impressively, he's already devoured about 22.5% of known universes that way.
 * This is the goal of in Justice League Crisis On Two Earths, once he learns of the existence of the multiverse. It is quite awesome, but ultimately foiled by Batman.
 * Attempted by Spider-Carnage in Spider Man the Animated Series. Driven mad by the deaths of everyone he cares about, and possessed by the Carnage symbiote, an alternate universe Spider-Man attempts to, in his own words, "Destroy all reality." His plan is basic: utilise one of the Spot's vortexes to absorb the entirety of Earth, any Earth. The absorption of the planet will then trigger a bomb similar to the Davros example, destroying Earth, and amplified by the portal, the universe. It doesn't end there though. Oh no. With the portal still open, the blast will be replicated across the entirety of the multiverse, ensuring that when Spider-Carnage dies all of creation dies with him.
 * Done as a joke for an intro to The Simpsons, where aliens create a wormhole that's powerful enough to even suck God into it, leaving nothing but a blank slate.

Other

 * According to Solipsism, your mind is the only sure thing to exist. In Metaphysical solipsism, everything else is just a part of your reality. When you die, all of reality is destroyed with you.