From the very first chapter, "Luna vs. the Microwave": Ideal amount of time to microwave popcorn? Twenty seven minutes!
At full power.
Luna's hilariously verbose attempts at heckling the opposing team's pitcher and the umpire in "Luna vs. Baseball".
Similarly, her sesquipidellian attempts at cheering on the cloudball game in "Luna vs. Ponyville, Part 4".
In "Luna vs. Lodging, Part 2", a blissfully unaware Luna gets taken to a seedy bar by two colts. One of them starts coming on to her just a bit too much. Luna proceeds to nuke the living hell out of the bar.
Afterwards, the Gilligan Cut to Sundance's boyfriend Hoyden during Sundance and Luna's post-bar explosion discussion
Hoyden: Note to self, no matter how hot she is don't suggest a threesome. EVER.
The reveal in "Luna vs. Communication" that Hoyden's Cutie Mark is the Jackass logo and that his job is testing safety equipment... by pulling crazy stunts.
Luna's phobia of baseball, and the circumstances that caused it.
Which leads to an amusing Brick Joke in "Luna vs. Lodging, Part 3" when Sundance tries to invite Luna out to get her out of her shell.
Luna: What is i- AAAAAAAAAAAAH! *Slams the door to her room*
Sundance: *Decked out in a jersey, hat, mitt, and holding a baseball* What was that about?
Luna's Imagine Spot of "Trollestia" banishing her and her abacus to the moon again for ruining the microwave. Come to think of it, every Imagine Spot so far is hilarious.
The one in "Luna versus Communication" especially: Sundance and Hoyden imagine Luna as a Dominatrix. Hoyden's drooling reaction is just icing on the cake.
Follwed by Holden's Imagine Spot of Princess Luna dressed up in cattle wrangling gear.
A pretty funny moment pops up in the Imagine Spot during Luna and Big Mac's blind date in "Luna Vs. Lodging 3". Four words: Pony shaped fighter plane.
"Oh Big Mac, I can no longer contain my crazed lusts for your handsome, broad body!" Luna cried dramatically, falling back as she held a hoof to her forehead. Big Mac caught her, his face extremely stoic.
"Eeyup. Same here. Come away with me, my alicorn angel. We will away in my pony shaped fighter plane," Big Mac said, rolling his head in the direction of said craft. Luna gasped.
"Oh my! I didn't know you had a pony-shaped fighter plane!"
"You never asked. Now I have to head off and fight in some war, cause that's what I do," Big Mac said. Luna was suddenly standing in a wedding dress and crying.
"You'll come back, won't you?" Luna sobbed.
"I might, might not. You'll wait for me, right?" Big Mac asked. Luna nodded.
Big Mac slipped on some sunglasses and trotted off to the plane.
"You'll never see him again! Just as you'll never see me again!" Abacus yelled.
The Doctor and Derpy's cameo where they return her Abacus, which Celestia let them borrow.
"Sorry, can't say anything. Thank you for letting me borrow it," the colt said. "Well! Not borrow, borrow without asking, I need to stop doing that anyway! Your sister sends her apologies that she let me borrow it without asking you after the fact... It's complicated and right now five things and a lizard are all happening at once so really we must be off. Hello! Goodbye!"
Luna mock fighting pink plushy dragons for "training" against real dragons. Celestia's reaction makes it clear that she just made Luna do it because she thought it would be cute. Possibly inspired by this piece of fanart.
"Luna versus Ponyville Part 1: Television" has the reason Luna's back in the castle: She walked in on Hoyden and Sundance having sex.
Luna's paranoia about Pinkie: "She could blend in and attack like a pink cobra..."
Luna's nightmare in "Luna vs. Ponyville, Part 3." Especially the bit where she dreams about Abacus cheating on her. Source of some hysterical laughing fits.
Luna's Imagine Spot in that same chapter features Rainbow Dash lamenting she and a dying Pinkie Pie were going to adopt a child, then insisting that she isn't gay and SHE WILL DO EVERY COLT IN EQUESTRIA TO PROVE IT!
Rainbow Dash asks Luna what she does for fun in "Luna vs. Ponyville, Part 4".
Luna: ...I have an abacus?
And she later asks Luna if she has a pet.
Luna: ...I have an abacus?
Before "Luna vs. Lodging", Luna did many things for fun that were actually work. Among these, she did calculations for the space program, reorganized the irrigation system of an entire province, established a new system of emergency response and management for the whole kingdom, and made sense of the tax code. Celestia is puzzled about the last one...
Angel Bunny channeling Patton in "Luna vs. Ponyville, Part 5." Complete with a carrot in place of a cigar and a tank that shoots baseballs.
Luna tearing up over half of Pinkie's house, thinking she's going to bake her into Cupcakes
Shortly after, Fluttershy revealing a lot of Hidden Depths as she explains well thought-out arguments that Luna's mountains of paperwork in her effort to make the kingdom more efficient are also doing damage to it, such as centralizing government making it more effective but also reducing the freedom the civilian population has while also leading to excessive bureaucracy.
"Luna vs. Ponyville, Part 6" has Fluttershy using psychotherapy to help Princess Luna with her fear of baseballs... with the over-eager assistance of Applebloom. Applebloom as Princess Celestia during the "role-playing" session has to be seen to be believed.
Better still is Luna getting even with Angel.
What an angry Luna does to a Kong and a Rex in "Luna vs. Ponyville, Part 7" when they wreck her old palace in the Everfree Forest and threaten the Cutie Mark Crusaders: shrinking them down to the size of mice.
It goes one better: All of the guards she brings in for the orgy are named after male porn stars. Implying she does this regularly. (And when Luna is not up for it... "I'll see you all on Friday.")
Hoyden and Sundance's state at the end. They've both too sore to move properly after their second threesome with Luna, which involved among other things Luna using a strapon. Also, Luna's freaking out when she realizes this took place in plain view of Abacus.
From the same chapter, Pinkie Pie telling Twilight Sparkle about the porno that Celestia sent to them (one she lent to Sundance earlier).
Don't forget Sundance's imagine spot of Big Mac's... Trouser Snake.
(Paraphrased) It moves!? OHMYGOD IT'S GOT ME SOMEPONY HELP oooh it's so dexterous AAAAAAHH!
"Luna vs. the GGG", in which Luna has a crazy dream about Big Macintosh and Abacus fighting for her love.
"Ponies in Space" opens with Luna getting rather excited about creating a method to prove the transcendence of irrational numbers. "EUREKA! I AM THE GODDESS OF MATH ONCE AGAIN!MWAHAHAHAHAHAHA!" Made even funnier that there's apparently a storm going on outside that has lightning and thunder to provide the perfect backdrop.
"Ponies in Space 2" brings us Sundance stealthily insulting Prince Blueblood in French:
"Tu es completement debile," Sundance replied flatly. "On t'a bercé trop près du mur?" "Yes, I would love some rice pudding," Blueblood said.
In order, she says "The brain was optional for you" "Reality and you don't get on, do they?" "You're a complete moron" "As a child, was your cradle rocked to close to the wall?" and "Your mother sucks bears in the forest."
There's also the peek at the Diamond Dogs' attempts at a space program: "Get me a bigger rocket!"
Also, Blueblood being put through the training.
Luna channeling the Eleventh Doctor in "Luna vs. Baseball."
"We're gonna smash em and crush 'em and destroy them!" Applebloom cried, standing up on her seat. Luna stared at her in horror.
"What? NO!" Luna spread her wings and flew up in front of the assorted ponies. She glared furiously through her glasses at the surprised fans. "You will do no such thing! I am the former Nightmare Moon, the keeper of peace and balance in the heavens and… And…!"
Applejack was waving her hooves frantically above her head. Luna looked around, and felt her cheeks burn in embarrassment.
"And… You were all speaking figuratively," she said. A number of nods and acknowledgements were thrown at her. "Right… Well… Um… Carry on," she said, flying back to her seat. She pulled her program up over her face and focused intently on the statistics of the players. Luna smiled in relief.
Sundance meeting the Elements of Harmony in "Ponies in Space 4", particularly Pinkie Pie.
"Ooh... Either you like candy as much as I do or you're pregnant! Congratulations if it's the second one, and double congratulations if it's the first!" Sundance stared, and her cheeks began to turn red. Her brows twitched. "... Dear, you can't murder one of the saviors of the world," Hoyden said, immediately massaging Sundance's shoulders.
The meeting about Mechapony-1, from Luna's flashbacks to her days of cliched villainy to the general spoofing of Humongous Mecha tropes: "Why shouldn't the giant robot have eye lasers?"
Even Fluttershy is in favour of the lasers.
"Ah well... I suppose I'll just have to steal [the Elements of Harmony] from her ...What's she going to do? Use them against me?"
Luna being unable to find any crime to foil as the Mysterious Mare-Do-Well in "Luna vs. Vigilantism 2". Even the Mafia is friendly and law-abiding.