While grieving her mother's death, young Queen Moon must make a decision whether to go to war or sign a peace treaty with the monsters. In the midst of this, she makes a deal with the Queen of Darkness, Eclipsa.
- Abhorrent Admirer: Count Mildrew is this to Moon, who clearly doesn't appreciate his patronizing attitude, his suggestion for her to "deal with her feelings" while he and the rest of the court handle everything else, and his pulling out her chair for her at the meeting.
- Adorkable: River is adorable in his attempts to comfort Queen Moon.
- Affectionate Nickname: Moon calls Glossaryck "Glossy".
- Ambiguously Evil: Eclipsa acts kind to Moon and empathizes with her over the death of her mother and being forced to take the throne at a young age. Moon even questions how evil she was after their encounter, although she visibly falters when reciting and using Eclipsa's The Power of Hate spell which is what causes it to merely graze Toffee. After all the sympathy Eclipsa shows her, Moon still can't trust her.
- Ambiguous Syntax: Eclipsa was in the same position once, and responds to young Moon's burdens of being queen with "I know how you feel". Is Eclipsa relating to being made queen at such a young age and having to decide the fate of Mewni? Or her inability to decide which boy she likes?
- Apology Gift: River gives Moon an "apology meat" (a chicken drumstick with the word "sorry" carved into it) to make up for his speaking out of turn at the meeting, adding that it's how his family apologizes.
- Bland-Name Product: The candy bar Eclipsa wanted is "Snookers", a spoof of Snickers.
- Body Horror: Eclipsa's hand is completely black from the use of black magic. Moon gets her own Tainted Veins from using the same magic to defeat Toffee.
- Both Sides Have a Point: Deconstructed. One side wants to go to war (Rhombulus, Mina) since killing a Queen warrants such a response but the other side (Omnitrax, Count Mildrew, and Hekapoo) say they should sign the peace treaty since that will quickly end the war. Either reasons for the side are valid and also can be counterargued, and the decision to decide what to do only puts more emotional strain on the young Moon.
- Call-Back: We finally see Moon's confrontation with Toffee, which was first mentioned in "Into the Wand".
- Chekhov's Gun: Eclipsa being part of the Rogues Gallery in Rhombulus' room becomes relevant when we see that Moon wished to learn a spell of hers decades ago.
- A Child Shall Lead Them: Moon became Queen at roughly Star's age due to Toffee killing her mother, the previous queen. In accordance with the trope, the High Commission doesn't even see her as their leader until she defeated Toffee and planned to stifle his followers.
- Continuity Nod:
- Back in season's 2 "Game of Flags", Moon's aunt mentions a Lord Mildrew. This episode marks his first appearance, but he was "Count" at this point.
- Mina Loveberry is part of Queen Moon's court in the flashback, hence why Star revered her as a great warrior. She was still a little off back then, but time obviously hasn't been kind to her.
- Queen Moon rides Li'l Chauncey to the meeting with Toffee, as shown in "Into the Wand". He isn't covered in arrows, so that was evidently an embellishment on the tapestry.
- Rasticore is among Toffee's soldiers. He allows one monster to bite off his arm (the one that has been replaced with a mechanical arm in the present) to show off their regenerative abilities.
- Deal with the Devil: Moon makes a pact with Eclipsa in order to learn the spell she used to destroy Toffee's finger and end the war. In exchange, she promises Eclipsa "freedom".
- Double Meaning: When Moon is talking about all the responsibility heaped on her when she can't even decide which boy she likes, Eclipsa says "I know how you feel." On the surface it seems like she's talking about the responsibility, but Eclipsa's infamy did come from her choosing her monster lover over her Mewman one.
- Dramatic Wind: Count Mildrew's hair and cape flow with a nonexistent wind when he first appears before Moon.
- Dramatization: In-Universe, this seems to be the deal with Moon's tapestry depicting her battle with Toffee. In their actual confrontation:
- Li'l Chauncey was not covered with arrows.
- Moon didn't have a look of utter hatred in her face, but rather a fierce concentration in her eyes. She also wasn't mounting Chauncey.
- Toffee wasn't bearing an expression of fear in his face. Upon realizing his finger wasn't growing back, he showed a mild annoyance and simply left the battlefield (though his troops, on the other hand, were visibly terrified).
- Moon wasn't shooting down at him from the air. They were on even ground, standing in front of each other.
- The Dreaded: Despite being the one who froze her, Rhombulus runs as soon as he's partially freed Eclipsa so Moon can have a chat.
- Exact Words: Moon didn't free Eclipsa because she crippled Toffee instead of killing him, and the contract said that Eclipsa would be freed "after Moon's enemy is dead."
- Forgot About His Powers: No one brings up the idea of Rhombulus putting the Septarians in Crystal Prisons (although the army may be too large for him to handle it all himself).
- General Ripper: Mina Loveberry has this air, being overly brutal with the monster monarch during his confession, and insisting that the Mewmans need to go to war with the monsters.
- Hair Flip: Mina whips the monster monarch with her pigtails.
- I Did What I Had to Do: Moon offers no other justification for using a forbidden spell on Toffee.
- Immortals Fear Death: Toffee's followers run away in fear once they learn Queen Moon found a way around their Healing Factor.
- Inelegant Blubbering:
Count Mildrew: She was so young!
- Glossaryck weeps unashamedly while mourning the loss of Moon's mother.
- Count Mildrew breaks down when he sees Moon walking into the monster's camp.
- Interrogating the Dead: A variant in that Eclipsa wasn't dead, merely in stasis.
- Know When to Fold 'Em: After the spell Moon learned from Eclipsa blasts off Toffee's finger and he finds himself unable to regrow it, his army runs away and he himself decides to retreat.
- Lampshade Hanging: Moon, when first meeting Toffee, lampshades how utterly out of place such a name is for the monster who murderered her mother and threatens all of Mewni.
- Lesser of Two Evils: Ultimately, the position Moon is put in: due to her Deal with the Devil with Eclipsa, she has to pick between Eclipsa or Toffee, as killing the latter will free the former. Ultimately, she still can't trust Eclipsa enough to see her as this trope and chooses to cripple Toffee, but not kill him rather than free the Queen of Darkness.
- Madness Mantra: Eclipsa can only utter "B4" after being partially released. B4 being the code of a chocolate bar in a nearby vending machine.
- Magical Incantation: Whereas Star's spells usually function by just calling out their name and we've yet to see spells of Moon's own invention, Eclipsa's are based on rhyming incantations. Her spell she teaches Moon for killing an immortal goes like this:I call the darkness unto me
From deepest depths of earth and sea
From ancient evils unawoken
Break the one that can't be broken
To blackest night I pledge my soul
And crush my heart to burning coal
To summon forth the deathly power
To see my hated foe devoured
- Mass "Oh, Crap!": When Toffee fails to regenerate his finger, his entire army panics and runs away in fear.
- Never Say "Die": Everyone is dancing around saying "die" when talking about the late Queen, in part to try and spare Moon's feelings.
- No Saving Throw: The spell that Eclipse teaches Moon completely bypasses immortality. If it hits, it doesn't matter if you've got an insane Healing Factor or are a Four-Star Badass, you're dead, or at least maimed.
- Not So Stoic: During most of the episode, Moon is never shown crying over her mother, except in front of Eclipsa. Queen of darkness or not, she's still Moon's family member, so of course the young queen would feel comfortable enough to cry around her.
- O.O.C. Is Serious Business: You know things are bad when the normally chill Glossarick is crying his eyeballs out.
- Out of Continues: The intent of the spell Eclipsa taught Moon. It's explicitly for killing an immortal, and completely negates any form of Healing Factor. Even if it isn't used for a killing blow, it will inflict a Wound That Will Not Heal.
- Parental Favoritism: Well, more like mentor favoritism, but Glossaryck is shown deeply grieving Moon's mother and even remarked he really liked her. Considering all Butterfly queens, except Eclipsa, questioned his methods, she must have earned his respect and affection.
- Plucky Comic Relief: Rhombulus' childlike attitude and Mina's wackiness are the source of comedy in the tension heavy "Situation room" scene.
- Red Right Hand: Eclipsa frees her hand from the crystal and leaves her glove inside, revealing her right hand to be black with veins running up her arm. Moon's arms become the same (though not as extreme) after she casts Eclipsa's spell.
- Renegade Splinter Faction: Toffee was a rogue general who killed the previous queen while a peace treaty was being negotiated between the Mewmans and monsters.
- Self-Mutilation Demonstration: To show off the Lizards' Healing Factor to Moon (despite her objections), Rasticore has his arm bitten off. He then grows a new one and high-fives his old arm with it.
- Shout-Out: The candy bar Eclipsa asks is called "Snookers", clearly a reference to popular Snickers, and she only calming down after eating it is a reference to the infamous "You're not yourself when hungry" Superbowl commercial.
- Silence, You Fool!: Mina hushes the monster monarch during interrogation, saying he would "shut up during [his] confession".
- The Starscream: Toffee betrayed the monster monarch, and sought to make war with the Mewmans.
- Strong Family Resemblance: Young Moon looks exactly like Star does now, minus the hair color and cheek marks.
- Take a Third Option:
- Moon's options are continuing with the peace treaties despite her mother's murderer being on the rampage or restarting the war in retaliation for said murder. She ultimately chooses to defeat Toffee and scatter his army instead, taking retaliation only on the one actually responsible.
- Moon clearly intended to kill Toffee at once with Eclipsa's spell, but instead just crippled Toffee knowing that all the monsters' bravado was because of the Septarians' nigh invulnerability, so seeing their general incapable of regenerating destroyed their morale.
- Too Hungry to Be Polite: Eclipsa's first words when she regains consciousness, while still gasping for air, is an order from the vending machine across the room. And once she has the candy in her hand, she devours it like a hungry animal.
- Trickster Mentor: Glossaryck, whether on purpose or accident, gave to Moon the idea of seeking Eclipsa's knowledge by flipping the pages of the book until Eclipsa's chapter in order to cry in the chapter of Moon's mom.
- Underestimating Badassery: Toffee and his followers don't take Moon very seriously, and neither does most of High Commission. If it weren't for Moon choosing to simply maim Toffee so as to not release Eclipsa, she'd have killed him dead.
- What's Up, King Dude?: River keeps trying (and forgetting) to be polite and deferential to Moon now that she's queen, and is at one point mortified to realize he referred to her as "pal".
- Whole Episode Flashback: The entire episode takes place decades before the main series, showing how a young Moon learned her "darkest spell" and used it to defeat Toffee.
- Wound That Will Not Heal: The reason why Toffee never regenerated his finger is because he can't. The spell Moon used, designed to kill an immortal, vaporized his finger and made it so any attempt to regrow it would immediately rot the new appendage.