This takes place during the Season 2 Episode, Its About Time, when Twilight time-travels back to warn herself of herself.
Twilight Sparkle was confident in her choice to go back in time and let past Twilight know there was nothing to worry about.
She took the scroll from Pinkie with her magic, looked it over, and lit her horn, letting the ancient magic flow through her. Her horn began taking on an over-glow, but she disappeared in a flash of light before it was fully able to.
When she opened her eyes and looked around, this was not the past she was intending to go to. This wasn't even the past.
"What the-... Where am I? This isnt the-" Twilight began, but she was cut off by a voice on a loudspeaker. It carried a playful, yet sensuously deceptive tone. A familiar tone.
"Welcome To the T. A. D. A., the Temporal Adjustment and Displacement Agency. One moment while I find you an Agent."
"... I've never heard of-" and Twilight was cut off again, this time by Discord appearing next to her. "Welcome, and thank you for choosing me as your agent!" Discord grinned at her, giggling a little to himself. "What are you doing here, Discord!?" Twilight demanded, attempting to light her horn, but failing.
"I am Discord Number 6,529, and I will be leading you through our great facility today."
Twilight balked a little, growling. "I didn't choose you as my-" Discord cut her off with a finger.
"shush-shush-shush. It doesnt matter regardless. If I started making sense, it just wouldn't make sense. Does that make sense?..." Discord asked. Twilight was about to reply when Discord spoke again. "Of course it doesn't. Now, I have a little questionnaire for you as we make our way through the facility. In this facility, you are incapable of lying, and you will always be guided to your correct destination. The questionnaire is only for insurance and liability purposes."
"O-okay..." Twilight wasnt sure if she should actually keep going, but her hooves began trotting forward beneath her without her control. "Agh! What's happening?"
"The System has taken control, and you are only capable of doing what the System demands of you. Our intent is far from malicious; we just had too many wanderers back in the day. Oh, the Chaos it was. Anyway. Question One: Is your full name Twilight Twinkle Sparkle?" Discord asked her as they walked.
Without thinking, Twilight replied, "Yes." and then realized it was not her that had said it. "Wait, how did- I didn't say that! Nopony knows my middle name! How did-"
"The System ensures Correct answers in the form of 'Tell No Lies'." Discord cut her off, answering mysteriously. Twilight just huffed and resigned herself to this 'questionnaire' Discord had.
"Question 2: Were you born on the 28th of Spring-Rain, 19 BLR1,2?" Discord asked.
"Yes," Twilight found herself answering. She frowned. "I'm serious, how do you know all of this? I haven't even told my friends my birthday yet. How do You know?" Twilight asked, still trotting along next to Discord.
"In this dimension, I know All. Question 3: Did you use the Temporary Time Travel scroll for malicious intent?"
"No. ... At least that's something I don't mind telling you"
"Question 4: Did you learn a lesson before you used the scroll?"
"Yes"
"Excellent! You're coming along well." Discord said. As they went deeper into the facility, more and more branching paths became apparent. They passed by a very large amount of alternate paths.
Discord had apparently noticed Twilight looking around. "All paths in this facility lead to different outcomes in different dimensions at different locations, with more being created every second. If I showed you just your branching paths..." discord trailed off, and suddenly, there were many thousand less paths to take. "There ... Just don't ask me to show you all the other you's. One of you had a panic attack, and that left a mark on your memory. you may or may not start to remember it."
Twilight's brain began to hurt, more from what Discord had said than from her own memory playing tricks on her. "That doesn't make sense."
"All of the you's from all times and all dimensions are brought to right here and right now. But only when you tamper with time. I, myself, can see all of you. and there are millions. one or two are younger, most are older, and there are quite a few with-" Discord stopped himself. "oh, wait, I can't tell you about that."
"What is it you can't tell me?" twilight asked, her curiosity piquing.
"Sorry, it was a slip of the tongue. I forgot I was escorting a younger Twilight this time."
Twilight's eyes crossed from confusion. She shook her head to clear it, and they continued on.
"Question 5: Did you know that your logic about time traveling back to tell yourself 'everything was fine, you don't need to worry' was flawed logic?" Discord asked.
"No, I didn't believe my logic was flawed. ... Wait, how was my logic flawed? I knew that worrying about the future was not as important as I thought it was, and I wanted Past Me to know about it."
Discord chuckled. "A perfect self-creating Time Loop. The Doctor would be proud of you."
"A ... Time Loop?" The gears in Twilight's brain turned anew. "... Wait, that's what I'm doing? Ah, Pony-feathers!"
"Indeed. Thankfully, we only have a few more questions before we get to your out-portal." Discord grinned to himself, having started to come up with his own questions. "Question 6: Did you ever have a crush on your brother?"
"A small one, but I grew out of it quickly... wh-whAT!? Why the HAY would you ask THAT!? I've been repressing that for years and now I remember it. Ughhhhhh...." Twilight groaned. "you think you're soooo funny, don't you?"
"I like to believe so," Discord snickered. "Question 7: Which of your 5 friends is your favorite?"
"I enjoy my friendship with all of my friends. they all have flaws, they are all real, and they are all great in their own ways. I can't choose a favorite... wow... r-really?" Twilight smiled to herself, tearing up a little. "I didn't know I felt this way about them."
"You do, my little pony. You certainly do. Now, the Final question: Do you understand that you will only remember minuscule tidbits of this whole scenario?"
Twilight paused as she, for once, got an opportunity to think before answering. "yes, i do understand" 'nevermind' she thought. "wait, I wont remember any of this?"
"I'm afraid not, my dear. These are the Rules of The TADA." Discord replied, and they walked up to a portal door.
"Looks like this is goodbye." Discord chuckled, and before twilight could react, he booted her through the portal.
Future Twilight got up from the ground and shook her head, acknowledging Past Twilight. "Twilight, you've got to listen to me."
And the rest... is history.
Author's Note
1: Before Luna's Return
2: Assume BLR in Equestria is equivalent to BC on earth
