We all know the Makuta right? Giant protosteel titans who have 42 assorted powers?
In this retelling, the Makuta have been around for nearly 850 years and have been gaining power ever since. Not the "world domination" sort, but political power. While the Makuta are the protectors of the pony world, they also serve as advisers, politicians, and scientists for the Queen of the Sun.
While Celestia was apprehensive of the Makuta at first, over the years she came to trust them. She grew accustomed to their presence and individual behaviors, calling some of them friends.
Then, the day came when Twilight Sparkle passed her exam. A small seven-year-old filly with the potential to level the city, raise the sun and moon, and grasp concepts of magic that even boggled Celestia's mind.
Yet, all that magic.
And all that knowledge.
Would be gone in a matter of seconds.
Replaced by a mind for mechanical and biological science. And a body of flesh and bone, replaced by one of anti-dermis and indestructible metal.

Cover art commissioned by https://www.deviantart.com/azonbobcat