Fluttercruel: Chaos Theory: After being saved from Oblivion by her father Discord, Fluttercruel gets used to her new-found powers and bonds with her father. However, soon, an evil dwelling in the subconscious rises, and the one who formally cast Equestria into a chaotic hell and his daughter may be the only ones that can stop it.
Twilight: Puppet or Pony: A story from the point of view of the Twilight construct Discord created. As she goes about day to day life in Discord's and Fluttercruel's world, she gradually comes to wonder why she has memories that don't match up with the world she sees around her.
A.I. Is a Crapshoot: A benevolent version. While not computers, the construct ponies Discord makes to populate his and Fluttercruel's world begin to become more life-like, instead of only following simple instructions like they did before. Discord is not certain why they began to develop this way, as they never had before, but it's implied Fluttercruel's presence may be causing it. They even begin to develop beyond being simple copies, with Construct!Rarity beginning to make chaotically themed dresses on her own, seemingly without any prodding. Twilight: Puppet Or Pony confirms the constructs have become fully sentient.
Action Mare: Fluttercruel, the Chaos constructs, Celestia and Luna. The list is long.
Affectionate Nickname: As they begin to bond both Discord and Fluttercruel give each other these. She begins to call him "dad" while he starts to call her "my little princess." Subverted by the fact that she doesn't like this name at all but doesn't mind the new one Discord comes up with afterwards: "my little angel."
Alas, Poor Villain: Nightmare Phobia's death invokes this. In her final moments, she recovers her lost memories and realizes just how in the wrong she was. Her last act is to reach out to Celestia and Discord longingly before dying. Luna even mourns for her afterwards.
And This Is for...: Discord does this during the fight with Nightmare Phobia, name dropping the constructs of Rarity, Applejack and Rainbow Dash, who all died earlier in the fight.
Armor-Piercing Observation: Pony POV!Fluttershy manages to give one to Discord without even knowing that he is listening in to her conversation with Pony POV!Fluttercruel.
Fluttershy: You're lonely.
Assimilation Backfire: Nightmare Phobia's attempt to absorb Discord and Fluttercruel in order to feed off their Chaos energy backfires and weakens her instead.
The Assimilator: Nightmare Phobia can grow stronger by absorbing chaos energy, and thus tries to absorb Discord, Fluttercruel and the constructs. Then she absorbs the Shadows of Oblivion in order to go One-Winged Angel.
Bad Dreams: Discord has nightmares about the Dark World.
The Big Bad also creates those whenever she is around.
Batman Gambit: Discord and the Alicorns use this tactic a few times in the final battle.
Berserk Button: Discord becomes much calmer and balanced when he is together with his daughter. But when she is in danger…
Big Bad: Nightmare Phobia, Luna's Enemy Without. Not only is she the mane antagonist of the story she was responsible for many of the events of the show by increasing the fears of various ponies, including the mane six.
Bittersweet Ending: Nightmare Phobia is destroyed, and Discord and Fluttercruel make peace with the Princesses, but the Construct Ponies are all dead, leaving Discord and Fluttercruel alone in Limbo once again. Though the Constructs also managed to gain their own souls and earn a place in Pony Heaven and Fluttercruel manages to reconcile with Fluttershy with Luna's help. The last scene has Discord begin recreating Chaos, with Celestia offering her and Luna's help.
Boxing Lessons for Superman: Discord never learned to fly without his telekinesis and learns from Fluttercruel. This helps him conserve power while battling Nightmare Phobia.
Break the Cutie: Fluttercruel breaks down crying after being forced to reveal her true form to Fluttershy to scare her out of the nightmare Nightmare Phobia put her in, ruining Fluttercruel's only chance to get to know her mother.
Chekhov's Gun: Fluttercruel uses what she has learned about chaos and shape-shifting in Fluttershy's dream to save her from Nightmare Phobia.
All of Construct!Twilight's lessons on chaos magic come in handy for Fluttercruel during the Final Battle.
The mirror Discord creates to look into other worlds plays a role in the Final Battle.
The letter Discord had written for Celestia and Luna as a plan B ends up having a message for Fluttercruel (who he figured would take a peek). Said message ends up being key to Fluttercruel figuring out how to fight back and defeat Nightmare Phobia.
Chekhov's Gunman: Luna and Celestia have just a very short scene in Fluttercruel: Chaos Theory but become much more important later on.
Clipped Wing Angel: Nightmare Phobia's final form after being crippled by Fluttercruel subverts this as she is far from harmless.
Clones Are Ponies Too: Discord assures Construct!Twilight that even though she was created from chaos, she's still as real as the original Twilight.
Combined Energy Attack: Celestia, Luna and Discord use the Elements of Harmony to tap into the harmony of every living being in Equestria in order to destroy Nightmare Phobia.
Crazy-Prepared: Discord really does plan ahead. He prepares his daughter for a battle he know might happen, his present contains a tracking spell and his letter to the Princesses contains a message for her.
Cross Through: Discord's viewing of Dark World eventually happened in the main series, as did Liarjack's viewing of this world happen in this one. At the end, Discord witnesses Dark World!Twilight's redemption in the mirror.
Darkest Hour: The latter end of Discord: Complete Existence, as Nightmare Phobia goes One-Winged Angel by absorbing all the Shadows of Oblivion, overpowers Discord and the Princesses, and starts emerging into the real world, causing every living thing to suffer extreme pain.
It is hinted that the mere presence of the Big Bad there is slowly killing all living beings in the real world.
Dark Is Not Evil: Chaos is not evil and Discord's World of Chaos is capable of functioning perfectly and even supporting life when thought is put into it.
Divine Parentage: Fluttercruel is, like her main series counterpart, the daughter of the God of Chaos. Unlike her, however, she receives an infusion of chaos, giving her access to Discord's powers, as well as turning her into a Mix And Match Critter.
Emergency Transformation: Fluttercruel was severely injured while in Oblivion, forcing Discord to infuse her with chaos to save her. As a result, she becomes a Half Pony Hybrid with similar powers to him.
Emotion Eater: Nightmare Phobia feeds on the fears of ponies, while at the same time is able to increase said fears in order to manipulate them.
Enemy Mine: Celestia and Luna enter the void to help Discord and Fluttercruel fight Nightmare Phobia. By the time the fight's over, the Princesses have accepted Discord's Heel-Face Turn, and his friendship.
Foil: Fluttercruel is this to both her alternate selves from the original series. She's much more well adjusted than her main timeline counterpart and has a good relationship with Discord where that version truly hates him. She also genuinely seeks to have a good relationship with her mother, where the main Fluttercruel originally wanted anything but and only gradually learned to love her mother. On the flip side, she's not Ax-Crazy like Dark World Fluttercruel. This likely comes down to the fact This Fluttercruel was raised by a good Discord instead of Fluttershy or an evil Discord.
Fluttercruel does share a few similarities with her alternate selves as well. She has her very own Cruel to Be Kind moment when she has to shock her mother out of the trap the Big Bad set for her and in the Final Battle Fluttercruel shows that she is not only very able to fight viciously against the Big Bad but she is also able to bear the cruel events that she experiences in this battle, especially the death of all the chaos constructs.
Not to mention what's developed recently in the Dark World. Both Fluttercruels have an extreme devotion to their fathers, and both learned to use chaos after getting some of his power. The difference being that Chaos Verse!Fluttercruel learned to channel that chaotic power for the sake of Equestria, while Dark World!Cruel ended up becoming a Draconequus who tried to destroy reality in order to protect her dad.
Forbidden Chekhov's Gun: Discord's "easier way" to create chaos. In the battle against Nightmare Phobia it is shown how dangerous it can be. Fluttercruel manages to use it correctly to light the Darkest Hour and earn her Cutie Mark.
Celestia also sees a version of herself that rules Equestria as a dictator, crushing all opposition.
"Get out of Jail Free" Card: Subverted. The Princesses accept that Discord has been redeemed, but also that that doesn't absolve him of his crimes, and he agrees and will stay a thousand years imprisoned. But he doesn't mind, since he'll have Fluttercruel (who is permitted to leave into the Subconscious with Luna's guidance) and be able to recreate Chaos with the Princesses' help.
Heroic Sacrifice: All the constructs in the copy of Ponyville, except those of the Mane Six, allow themselves to be absorbed by Discord and Fluttercruel in order to give them the strength to fight Nightmare Phobia.
In the end Discord is also ready to make one but instead it triggers the above mentioned Combined Energy Attack.
Hope Spot: We get two close together in Discord: Complete Existence. First, Discord and Fluttercruel seemingly defeat Nightmare Phobia, only for her to absorb the Shadows of Oblivion and go One-Winged Angel. Shortly after that, they and the Princesses destroy her second OWA form, only for it to turn out to be a puppet of her true form.
Idea Bulb: Discord has one of these when Construct!Twilight says she wants a companion (like Spike to the original Twilight). It promptly grows wings and flutters off.
Ironic Echo: "A weighty choice is yours to make, the right selection or a big mistake", this time said by Discord to himself when having to choose between letting Nightmare Phobia kill Fluttershy and risking Fluttercruel's life to save her.
"Make sense? Oh what fun is there in making sense?" Twice, first when Fluttercruel says it to scare Fluttershy out of her nightmare, the context making it a tear jerking and second when Discord realizes he's a Bearer of the Elements of Loyalty and Laughter.
Knight of Cerebus: The stories are pretty lighthearted until the Big Bad shows up and tries to drive Fluttershy to suicide.
Nightmare Phobia is killed by Discord and Fluttercruel and goes to Oblivion, but pretty much eats the Shadows of Oblivion to go One-Winged Angel and escapes.
Love Redeems: Both Discord and Fluttercruel not only discover that Good Feels Good but their familial love for each other motivates them to take the next step. Discord unseals Celestia's and Luna's full power to make up for what he had done to them in the past, which allows the two Alicorns to come to his aid in the Final Battle. Fluttercruel starts to care more for her mother, soon she cares enough for Fluttershy to come to her help when the Big Bad is trying to kill her.
Made of Explodium: Chaos constructs will spontaneously explode if their creator loses their focus, at least if they're inexperienced. Discord doesn't seem to have this problem anymore while Fluttercruel has it when she first starts using her new-found power.
This comes in handy fighting Nightmare Phobia, as embedding something in her body then letting it explode causes considerably more damage with the bonus of making her incapable of absorbing it.
Meaningful Name: Celestia, Luna and Discord of course. Nightmare Phobia is another example.
One-Winged Angel: Nightmare Phobia goes through several stages of this after absorbing all the shadows in Oblivion. First, she turns into a giant hydra. When that's not sufficient, she turns into a literal Shadow Archetype of Princess Luna. When that's defeated, it turns out both forms were just puppets of her true form, a sentient, all consuming void.
Papa Wolf: Discord becomes this towards Fluttercruel after adopting her.
Pony Mom, Non-Pony Dad: Fluttercruel. She sees Discord as her father and Fluttershy as her mother. This is what causes her to save her mother from Nightmare Phobia.
Power at a Price: Nightmare Phobia becomes more powerful the more fears she absorbs but she also loses her memories of her former life as this goes on and becomes more and more insane.
She also manages to go One-Winged Angel by absorbing the Shadows of Oblivion. While this is a massive power boost, the fact that she relied on the Nothingness means that when she's defeated, she ends up dragged into Oblivion permanently.
Roaring Rampage of Revenge: An alternate version of Destruction goes on one of these against his family after he kills and eats Discord when the latter tries to do the same to him. To make matters worse, he's now just as powerful as Discord is...
Sadistic Choice: Discord realises that he is trapped in one when he has to choose between letting Nightmare Phobia kill Fluttershy or risk Fluttercruel's life to save her.
Sanity Slippage: Luna (though she gets better) and Nightmare Phobia (who doesn't).
Shout-Out: Several to the Pony POV Series happen over the course of the entire story:
Discord sees the Dark World and the Gaia arc of the main Pony POV timeline in Truth.
Discord finds Fluttercruel trapped and dying in Oblivion.
Fluttercruel has a similar train of thoughts to her Pony POV counterpart as she names herself.
Discord knows about the identity issues of the Pony POV version of Fluttercruel and the sadism of Fluttercruel from the Dark World and tries to avert this with his own daughter. He succeeds.
Similar to her Pony POV counterpart Fluttercruel can see famous dark fics like Cupcakes in her dreams. At first she just laughs it off but this changes once she realises that she could end up like that Pinkie Pie as well.
Discord has nightmares of the Dark World, seeing the scene were Twilight and Applejack report back from the slaughter at Ponyville.
The scene between Discord and Fluttercruel shown in Liarjack's journey through Truth in the Pony POV Series happens here as well.
Discord's Nightmare Night costume is a reference to the shape Discord from the Pony POV Series took while he was corrupting Diamond Tiara and Fluttercruel's costume is either Pony POV or Dark World Fluttercruel. She notices the irony.
Fluttercruel reveals herself while saying "Make sense? Oh, what fun is there in making sense?"
In Truth Celestia sees Shining Armor marrying Pandora instead of Cadence, who died a long time ago in the war. Anarchy and Strife are there as guests as well.
Celestia also sees a continuation of a story written by Kendell2 were Celestia's and Luna's roles are reversed.
In another vision Twilight Tragedy ends up replacing Discord as the ruler of chaos in the Dark World. Somehow it manages to be slightly less horrible compared to his rule.
In another vision the Elements manage to defeat Celestia's fallen brother Morning Star with the Fires of Friendship.
Finally Celestia does see how her Pony POV counterpart lived and eventually ended up in Equestria.
Fluttercruel's first chaos constructs take the shape of weapons similar to what the Element of Cruelty does. There is however one important difference with these weapons.
Shut Up, Hannibal!: Chaos Verse Discord gives one to Epilogue Discord simply by thanking him for showing him the end of his dark ambitions and saying that by extension, HE saved Fluttercruel from Oblivion.
Spanner in the Works: Pipsqueak ends up being this to Nightmare Phobia's plan to isolate Luna from Ponyville through fear.
Discord and Fluttercruel end up ruining her plan to drive Fluttershy to suicide.
Start of Darkness: Luna and Celestia: Unwanted Half is this for Discord, Luna and Nightmare Phobia.
The Dead Have Names: The Construct Mane Cast are given a memorial as the first thing Discord makes when recreating Chaos, followed by a pillar inscribed with all the deceased Constructs who gave their lives defeating Phobia.
This Cannot Be!: One of the worlds Celestia sees in the Truth is Morning Star nearly defeating the Mane 6, only for them to tap into the Fire of Friendship and destroy him. Naturally, this is his response and last words.
Tranquil Fury: Discord when Fluttercruel's life is in danger, the chaos constructs have a similar reaction.
Undying Loyalty: The constructs — especially those of the Mane 6 — to Discord and Fluttercruel.
Villainous Breakdown: By the time Nightmare Phobia goes One-Winged Angel, she's completely lost what little sanity she had left and turned into an Omnicidal Maniac. When the Final Battle begins to turn against her, she completely falls apart, going from threats to begging for her life, trying to convince the heroes to spare her life.
Villain Episode: Most of the third part of Luna and Celestia: Unwanted Half is written out of the perspective of the Big Bad
Villain Team-Up: Subverted. Not only has Discord long since had a Heel-Face Turn by the time Nightmare Phobia offers an alliance, but it's implied she knew he wouldn't accept anyway.
Villains Want Mercy: Nightmare Phobia begs for her life when the tide is turned against her. The heroes are Genre Savvy enough to know it's a trick and she'll just stab them in the back if they do.
"World of Cardboard" Speech: Fluttercruel gives one before using chaos to fight back against Nightmare Phobia and gaining her own cutie mark.
World of Chaos: Discord creates one in limbo, but this time much more structured and not as nonsensical, while still chaotic. It even has its own inhabitants. It helps this one actually had thought put into it so it'd be inhabitable.
World-Wrecking Wave: Discord is able to do this. It is actually the incomplete version of this ability, the perfect use of this is not destructive at all.
Year Inside, Hour Outside: Time inside the limbo that is Discord's prison, time moves much more slowly than it does in the real world. An exact amount of time isn't given, however.
This caused Celestia and Luna to be too late to help in the battle against the Big Bad but they are just in time for Nightmare Phobia's One-Winged Angel form
Your Worst Nightmare: Nightmare Phobia is able to enter a pony's dreams and cast them into their worst nightmare. This is how she almost drives Fluttershy to suicide. She tries to do this to Discord during the Final Battle as well, but he sees right through it.