I'm looking for fics along the lines of Six Little Words and Parting Words. Fics where Twilight, for one reason or another, gets fed up with Celestia's tests.

7509126 Firstly, none of what I'm about to paste is a perfect fit for what you're searching for. However, they do include some element of it.

In this one, Twilight deviates from Celestia's teachings and has a bunch of skeletons in her closet. She works in her own ways under Celestia's radar.

TSweetie Belle Gains a Soul

• MLP: FiM
• Adventure
• Drama
• Slice of Life

In her darkest hour, Sweetie Belle finds salvation, but it comes with a terrible curse.

• Twilight
• Rarity
• Sweetie Belle
• CMCs

Bad Dragon · 132k words  ·  178  45 · 6.8k views

Even more so in the sequel.

This one explores what the world would look like after Twilight stops being Celestia's student and takes over Equestria. It's administration galore.

TThe Ultimate Supreme Administrator

• MLP: FiM
• Dark
• Drama
• Tragedy

To be a High Administrator, that is my dream.

• Twilight
• Mayor Mare
• OC
• King Sombra

Bad Dragon · 3.8k words  ·  18  15 · 631 views

In this one, Twilight's deviations from Celestia's ways actually almost save the world. Almost...

TSupernova Daybreak

• MLP: FiM
• Dark
• Drama
• Tragedy

The sun is going supernova. Is there a way to save Equestria from the looming inferno?

• Death
• Twilight
• Spike
• Celestia

Bad Dragon · 4.4k words  ·  62  31 · 2.4k views

In this one, Twilight expands her horizons with books about how to rule. This includes King Sombra's Ruling 101.

TPrincess of Friendship

• MLP: FiM
• Drama
• Tragedy

After Twilight’s stream of successes, she’s confident that nothing can go wrong. Is she due for a lesson?

• Twilight
• Spike
• Main 6

Bad Dragon · 5.4k words  ·  290  46 · 7.9k views

I personally enjoyed this one: https://www.fimfiction.net/story/384960/twilight-gets-a-puppy