Luna crept through the dark hallways. Normally during this time she would be visiting dreams and ruining her sister's sleep, but Luna had decided to have a little fun. She glanced up at the clock on the wall. It was illuminated in the moonlight.
One o' clock in the morning. Good. Only her bat guards should be awake at a time like this.
Checking to see that nopony was watching her, she ducked into Celestia's office. Playing pranks was something Luna only did in her sister's dreams, but after the pie incident, she was going to get Celestia back big time!
"Now where did Celestia get her hooves onto technology as advanced as this?" Luna mused, picking up a security camera. She stared into the camera, made a face, and then turned it off. Nopony must see the mess she was about to make.
Levitating the papers into the air, Luna muddled and jumbled their order and left them on the floor. Then she thought she might read a few of them.
Most of them were letters of thanks from her subjects. Luna felt a jab of hurt. Their subjects never wrote to her. She picked one up with her magic and read it out loud.
"Dear Princess Celestia
We are most grateful for your hard work to
keep us subjects safe. We understand the
pain and the difficulties you must go
through every single day while you labour
tirelessly for us mere ponies. Your sister
Luna doesn't do nearly the amount of work
that you must do every single day. In fact,
I bet that you would easily be able to
raise the tiny moon in her place! Anyway,
we are eternally grateful for your efforts.
From Daisy"
"Well she's just trying to upset me," Luna snorted, grumpily. She had had no idea her subjects felt that way about her. Well, she had better get to work than.
***
Half an hour later, Luna had drawn on half of the letters the ponies had addressed to Celestia and messed them up completely. She had also found an order for seventeen chocolate donut cakes and thirty four caramel mud cakes with seven layers and strawberry icing.
"Well now that I know of her secret stash I shall be sure to come in here a lot more often!" Luna laughed after she found an enormous pantry stocked with cake of all flavours! Donut cakes, ice cream cakes, Hearths Warming Eve cakes (pretty early for that), and banana cakes. Lots. Of. Banana cakes. Luna had counted fifty seven when she remembered what she was there for.
"Right. The pranking." She looked at the enormous piles of cake in front of her. "Lucky I had a small supper," she cackled as her stomach rumbled. As Luna plowed in, she thought about how lucky Celestia was to have a sister like her.
***
When she decided she had eaten far more than enough, she sat down and contented herself by reading out more of the stupid letters the ponies had sent her sister.
"Dear Most Beloved Princess Celestia,
I love what you do for us ponies. You raise and
lower the sun everyday! I think it is amazing how
you do so much work every day without even
getting tired! You barely seem to eat anything
you work so hard! I love your sun and your
beatiful day so keep up the amazing work!
From Sweetie Drops Bon Bon."
After a few tweaks from Luna's pen, the note was something entirely different.
Dear Most Beloved Stupid Princess Servant Celestia
I love hate what you do for us ponies idiots.
You raise and lower the sun boring yellow dot
everyday! I think it is amazing lazy how you do so
much little work ever day without even getting
and your always getting tired! You barely always
seem to eat anything everything you work so
hard slow! I love hate your sun and your
beautiful ugly day so keep up the amazing
terrible work!
From Sweetie Drops Bon Bon idiot
"Much better," Luna giggled. Glancing at the clock, she realised she did not have a lot of time left before Celestia woke up. A few hours would not be enough to do everything she had planned. Oh well. She could still ruin a few more of Celestia's things before dawn.
The next thing Luna raided was her sister's wardrobe. There was the usual in there, ugly dresses (Luna had them too), gala gowns, bath robes, you know, that sort of thing. What Luna didn't expect to find was a banana costume. Really. A banana costume. Big, yellow, it even had holes for the wings! There was still a price tag attached to it.
Banana costume
CHEAP
447,886 bits
"And she says that I waste my bits," Luna snorted. She then went on to dance around in Celestia's banana costume while trampling on the papers that were all over the floor. Luna had even more fun when she discovered a radio in her sister's office. It already had a CD in it. Luna pressed play, grinning like a lunatic. 
I'm a banana.
Your a what?
I'm a banana. I'm a banana. I'm banana. Ahhhhhhh!
Luna almost died laughing when she heard what her older sister listened to in her spare time. It was quite a ridiculous sight, Luna rolling around, laughing in a banana costume on the floor with that music playing in the background.
When she finally came around she decided it would be best if she hurried up and got out of the office. So Luna decided to finished off with one more prank. The posters. There were tons of them. Celestia had posters of herself all over the castle, but there weren't nearly as many around the castle as there was in Celestia's office. And by the time Luna was done with them, boy, she would get a kick out of her sister's reaction!
***
Yawning, Celestia blinked her purple eyes open. "Goodness, what a lovely sleep!" She said to herself, sounding genuinely surprised. "It seems Luna left me alone tonight! That's the best nights sleep I've had in weeks!" Stretching, she climbed out of bed and brushed out her mane, feeling happier than she had ever felt after waking up. She trotted down the hallway and went to her office. She was planning on writing back to a few of her subjects. When she got there, her jaw dropped open.
"Luna.... Luna," Celestia gasped, rubbing her eyes to see if she was still dreaming. There was paper all over the floor, with Luna's handwriting all over it. Her pantry was open showing mountains of half eaten cake. Her banana costume was on the floor and her radio was still playing faintly. Her security camera was on the floor with a picture of Luna making a rude face stuck on the screen. She snatched up Bon Bon's letter and read it. Grinding her teeth together, she was about to scream out at the top of her lungs when she saw her posters.
Her posters. Her posters! HER POSTERS! They had permanent marker all over them. They had moustaches and rude words and hats and arrows sticking out of her head.
Celestia's face went red and she began to breathe heavily. "Keep calm... Deep breaths..." Then she saw an enormous, Luna-shaped hole in the wall. "Alright, someone's getting their butt banished!" Celestia shouted, stomping her hoof.
