Great-Greatest Grandmother of Celestia

Twilight Sparkle, local Princess Of Friendship, was going to experiment with pony magic, and why certain ponies can only do certain things.  She levitated her ancient books over to her side and began reading. The first spell was hard to read, since it was in Old Equestrian. But she managed to translate it into this:

MAGIC BOTTLING SPELL

For what sleeps deep in one's heart,

Come out now with any sound from a fart

to a dizzying tick-tock

or a bleating sheep

Do not sleep, do not sleep!

Come to your carrier's hooves so they

Can allow you to rise and obey

their command to contain you

Outside your body,

the only thing left, pure and bejeweled.

She began to halve the spell and divide it, and began to mix it up with the same cloning spell used in the Mirror Pool.

Twilight never got it to work until she went out and returned with pure Mirror Pool water. She cast the magic bottling spell and bottled her Pegasus and half of her Earth Pony magic, causing her wings to disappear and a ball of purple magic appeared in the jar in front of her. She opened the jar and placed the magic on the floor, and dumped one teaspoon of the magical water onto it. It began to spin and expand, and take the shape of a pony. When the light of the magic faded, a Pegasus Twilight Sparkle stood in front of her.

"What are you?" the purple ponies said at the same time.

"You're me... as a different race!"

"How about we go have a fun day together? But after today you have to go back inside me forever.I'm... so sorry..." Twilight choked in between sobs.

They ended up having a fun outing, drinking milkshakes and spinning until they were dizzy out of their minds.

But the time came, and the Pegasus went back inside Twilight's body, returning her wings and the other half of her Earth Pony magic.

Twilight went to bed, upset that her friend had to go.