Nightmare Mircalla doesn't care about her undead allies, seeing them as abominations, but is scared for the others, like her vampire followers, the dire wolves, and the few living sorcerers. As she is carried in her tent to their destination, she thinks about what will happen next. If they win, Nightmare Moon will return. Many on both sides will die in the process, and Nightmare Moon will likely turn them into zombies as well. If they lose, Celestia's followers will wipe them out. Most of her followers aren't even fighters and don't want to be here, but they will be killed for treason if they try to leave. She wonders how Sunset Shimmer and her companion will factor into this.
Her maid Spotless tells her they have arrived. Mircalla notes how scared Spotless is and how ill-fitting her armor is before facing the army. Before them is the entrance to a cave. She explains that this cave system leads to the caverns under Canterlot, and since the entrance is in the Everfree Forest, nopony knows about it. Once they reach the underside of Canterlot, they will plant this. Some warlocks throw aside a tarp and reveal a massive chunk of obsidian with a lunar symbol. It is a mana bomb provided by Mizu with a yield of 1000 tons of dynamite. It will be enough to blow Canterlot sky high. The army roars in approval. She orders the undead to enter the cave first to clear out any Everfree beasts that live within. The rest of the army will stay here to guard the entrance until they are done. She unenthusiastically declares, "For the True Goddess." but the undead roars it loud and clear as they move to follow her instructions.
She looks out at the rest and sees that her vampires are all scared and clearly don't want to be here. She orders the warlocks to step forward. They ask why they aren't leading the charge into the cave, and she says she has a special job for them. She creates a magic circle with runes on the ground, noting that her armor has boosted her magic significantly, and tells them to step into it. They do and vanish into thin air.
Rodan wakes up to find a sleeping Sunset hugging him. He's honestly surprised that when she wakes up, instead of getting mad at him, she quietly asks if he's still injured. Something's changed ever since she saved his life from the enhanced zombies, and she's no longer the haughty princess with a hair trigger temper.
The two begin searching for the Nightmare Army. He helps her cross a fallen bridge by carrying her and she thanks him. He comments that she's acting really nice, and she says her earlier attitude nearly got them both killed, so she's dropping it. He comments that her nicer attitude reminds him of Princess Celestia, and he likes it. She suddenly realizes something. After Mircalla killed her birth mother, she was dropped off at an orphanage. How did that happen if Mircalla was trying to capture her? He shrugs and says they can always interrogate Mircalla after they defeat enough of the army to signal Celestia, who should be powerful enough to defeat her. Sunset doesn't want Mircalla to be allowed to live a second longer than necessary and says they'll cross that road when they come to it.
They continue walking, but are forced to dive behind some bushes when a huge flock of bats and several dire wolves move past them in the opposite direction until they are out of sight. Surprised, they check where they came from and find the cave. Aside from some shredded leather that looked like it had once been reins and a burned circle etched into the ground, there wasn't a single sign the army had been through this spot aside from all the prints. Sunset identifies the bats as vampires, but deduces Mircalla was not with them, as her hoofprints, identifiable by their size and shape, lead into the cave. Rodan launches a small fireball into the cave, but it doesn't hit anything, meaning the army has already gone deep into the tunnels. Sunset notes vampires cannot disobey their makers and can command animals like dire wolves, so the ones that left are not deserting the army. The two have no idea why they left.
Several minutes ago, the vampires ask what happened to the warlocks. Mircalla says she teleported them to Whitetail Woods to get them out of the way. She destroys the dire wolves' reins with telekinesis and orders them all to go home. One vampire named Backsword points his lance at her and accuses her of treason, but she retorts the true treason was joining the Nightmare Army in the first place. She reminds them that she made them and they have to obey her. They reluctantly leave, and Backsword asks when they'll meet her again. However, as she enters the cave, she thinks of both Sunset Shimmer, who seeks revenge, and Mizu, who scares her. She says she won't see them again.
Sunset and Rodan enter the cave and she emits a flashlight beam with her horn. They soon catch up to the undead, who turn around and attack. They enact their Plan A.
The two blast each other at the same time to power up from all that accumulated heat. Rodan's body lights up with runes while Sunset's aura forms flaming wings on her back. They charge the army and burn through them like hot knives through butter. One Shadowbolt named Dark Thunder, a blood thirsty cannibal who had been killed centuries ago and now inhabits the body of a mountain climber Mircalla had put out of his misery, challenges Rodan, only to be destroyed almost instantly. The other Shadowbolts attack, but in his powered up state, Rodan can now Flash Step effortlessly, and he makes short work of them. Sunset is now so hot that the ground beneath her hooves is turning into lava, and the zombies are reduced to ash just by being near her. The undead warlocks stay back and try to blast the pair, but it is pointless. The ceiling soon collapses, letting in the light and crushing several with falling rocks.
Deeper in the tunnels, the undead warlocks and Mircalla have brought the bomb directly under Canterlot. They prepare a forcefield so that the explosion will be directed upwards. They hear the battle behind them. Mircalla orders them to take care of it while she arms the bomb, but when they turn around to obey, she suddenly turns into a swarm of bats and blitzes them, tearing them to pieces. She remembers the true identities of the bodies they inhabit, and now she puts them to rest. She reforms and listens to the battle, and thinks about that day she met Sunset Shimmer and her mother 20 years ago. It's time to finally do the right thing. She forms a saw-like blade with magic and swings it at the bomb, but Mizu emerges from a puddle and catches it with tentacles. It knocks her back and demands to know what she is doing. She attacks.
Sunset Shimmer and Rodan continue slaughtering the undead minions. Eventually, they perform a combination attack where he picks her up and they combine their blasts, firing in every direction. They fly through the hole in the ceiling just as rivers of lava engulf and finish off the rest. After the lava cools somewhat, they return and Rodan says they won, but Sunset says it's not over until they have Mircalla.
Mircalla, her magic amplified by Nightmare Moon's armor, battles Mizu, but the sea monster is incredibly fast and able to enter and exit reflective surfaces like the many puddles on the ground. It can emit a shriek that hurts her ears and rattles her mind. It hides in a puddle and converses with her telepathically. She says nopony can activate the bomb now and Princess Celestia is now out of its reach. She doesn't care if she can never remove the armor now. They hear Sunset and Rodan approaching and Mizu suddenly charges down the tunnel to attack them. Mircalla notes that the two most likely wouldn't stand a chance. She calls out that it made a mistake and swings her sword at the bomb. Just as she expected, Mizu emerges from the reflection of her armor and blocks it again. She quickly generates a black mist that shrouds the chamber in darkness. Both combatants can see in the dark perfectly, but without light, there can't be any reflections, so Mizu cannot jump through them anymore. She tackles it and the pair grapple. She creates a teleportation circle on the ground around them. Mizu, sensing this isn't good, breaks free and tries to escape into a puddle since the circle is glowing, but Mircalla bites it. Ignoring its supernatural coldness, she throws it into the circle and it disappears. Exhausted and with a broken leg, she staggers toward the bomb.
Rodan and Sunset enter the chamber to find the bodies of the warlocks and see Mircalla has just damaged the bomb with her sword, rendering it inoperable. Sunset is about to attack when Rodan stops her, sensing something isn't right. Mircalla introduces herself and says she was once an ordinary pony who went mountain climbing and was lost in a snow storm. Nightmare Moon came to her and offered her life and power in exchange for service, and turned her into a vampire. She now regrets it.
Rodan asks what happened 20 years ago. Mircalla says the warlock Apostle detected Sunset Shimmer's potential soon after she was born and asked her to retrieve the foal so that he could raise her as his own, saying it would be a test of her commitment to their cause. She attempted to use her gaze to paralyze Sunset's mother and erase her memories, but when she tried to leave with the foal, her mother suddenly broke free and tackled her. Unfortunately, the stress of everything she had just gone through was too much and she suffered a heart attack. Mircalla tried to save her but failed, but in her final moments, her mother seemed to understand her; she was only doing it to protect her coven.
Sunset starts crying, then she notices Mircalla had pulled out a silver sword, which can kill vampires, and grips it with her telekinesis. Rodan deduces that Mircalla was the one who took Sunset to the orphanage, and Mircalla confirms it. Conflicted, Sunset points the sword at her back. Mircalla walks backwards until she is touching it, and her skin starts to burn on contact. She says she doesn't expect to be forgiven, but Sunset should know her mother loved her. Sunset throws the sword aside and blasts Mircalla with light, but instead of destroying her, her armor falls apart, its dark magic nullified. Mircalla is shocked to find she is now free, and even more shocked when Sunset hugs her and says she is forgiven. Proud, Rodan gives the two some privacy. Eventually, Mircalla turns into swarm of bats and leaves. Rodan says he's sure both of Sunset's mothers would be proud of her.
At the mouth of the cave, Mircalla shields her eyes from the sun now that she no longer has the armor protecting her. Mizu appears, having traveled all the way from Appleloosa. It is about to attack, but she points out it could only stay in this world for 24 hours and its time is almost up. Bagan says this was but a minor setback and opens a portal for Mizu to return to Zenith. Mircalla looks up to see Princess Celestia flying down. She smiles and flies off to rejoin her coven.
As soon as Celestia had detected a massive surge of her daughter's magic, she immediately donned her armor and flew off to investigate. She arrives just as Sunset and Rodan emerge from the cave, then hugs Sunset and asks what happened and why she has tears on her face. Sunset says it's a long story with a happy ending. Celestia asks who Rodan is and he introduces himself. Sunset briefly explains that he's from another world and he saved her life. Celesta immediately hugs him. After a minute, Rodan's body sparks and he starts disappearing. Celestia scans him and says his link to the world is fading, and he's being returned to where he came from. Sadly, he likely won't remember anything. Rodan says for what it was worth, they made a good team. Sunset says she is sure they will meet again. He salutes them, and she kisses him on the cheek just as he disappears. Celestia comforts her, then asks if she should be expecting grandkids. Embarrassed, Sunset screams, "MOOOM!"
Life moves on. Mircalla returned to her coven, finally free of the Nightmare Army. Princess Sunset Shimmer had many more adventures in Ponyville, and her recent experiences helped heal her trauma and break her haughtiness. Rodan returned to his original Equestria and flew with Rainbow Dash in an airshow. Although he soon forgot everything, every time he sees a sunset, he remembers that warm smile Sunset Shimmer gave him before they were parted.
