Your gateway to endless inspiration
Was honestly thinking of playing with this in my dumb little AU thing, looking into the specific wording of the spell, with a very different Unicorn messing with the very same spell to try to finish their own ascension.
I thought it would be cute if that exact wording was turned around, and since they stubbornly hoard the elements trying to master them alone instead of sharing them, the spell would instead of swapping marks of their friends turns them into a Mark black-hole. In their quest to find fulfillment alone they'd turn themselves into a problem that keep accidentally "stealing" the destinies and Marks of those they get close too, until they're truly "singled out alone".
Undoing that and learning to actually share responsibility and power with others is the actual test of course, but its a different lesson for a different pony interpreted from the same spell.
Omfg I'm watching MLP "Magical Mystery Cure" and I had a thought
The spell twilight proforms, the one Starswirl The Bearded wrote it was
"the mark of ones destiny singled out alone, fulfilled."
The spell isn't about the elements, it's about Twilight. Celestial magic isn't what turns her into an alicorn. It's the spell. It's Twilights magic. It's her Destiny.
Switching the elements and finding the counter spell is just a test.