The mane 6 will not be in Ponyville when an antagonist appears. Such as, Discord, and they try to rule Equestria knowing the Mane 6 isn't there to use the Elements of Harmony. So, Princess Celestia selects a few ponies and brings them to her castle to discuss it or w/e. She tells them of the elements and how they will have to use them. They can't make it back to Ponyville though, which is where the antagonist is doing bad guy stuff. They came to her castle by the flying carriage thingy, but all of the Royal Guard went to try to fend off Discord. They aren't a match for him obviously. They have to go through Everfree Forest to on the way back. They have little moments when they discover their friendship and each of their elements. Then they use the Elements to defeat the enemy.
I was thinking of these:
Earth pony:
Bon Bon, Octavia, Doctor Hooves
Unicorn:
Vinyl Scratch, Lyra Heartstrings
Pegasus:
Derpy Hooves