"Alright. Don't worry, Princess. Let's put it to use right now."
Twilight looked up at the huge blood-red sun and activated Spherical Prison. A purple beam of magic shot upwards, through the temperature shield, at the sun. It began to surround the sun, then stalled, seemingly not strong enough. Slowly, the sun began to overpower Twilight and the spell.
Taking a huge risk by gambling on the safety of Canterlot in favor of the planet, Celestia stopped conducting her temperature regulation spell and helped Twilight with the spherical shield. Luna joined in to help by using a donation spell with Celestia.
It was working. The sun was no longer able to beat the shield and was soon trapped inside.
Although Canterlot was now flooded with near-lethal heat, the threat of the end of the world was suspended.
Twilight went to embrace Celestia and Luna in a hug of celebration. Celestia put her foreleg around Twilight as well.
"We did it! Equestria is saved! I just hope the heat wasn't too damaging."
"I am thankful I remembered that spell. It has been five hundred years since I've had to use it last."
Twilight's smile immediately faded, replaced by fear-filled eyes as she remembered a critical detail. She pushed herself away from their embrace. "Wait. Didn't you talk about an amulet?"
"Yes, I did. Why wou—" Celestia's eyes widened. "Oh no. That's why your practice spell didn't last long. Spherical Prison needs a medium to work properly."
"But why is it working, then?"
"I'm not sure. Maybe an amulet wasn't needed at all?"
"Well, how long will this spell last without the amulet?"
"I don't think it's ever been tested on such a violent scale like an aggressive sun."
"A dying sun," Twilight interjected.
"It could be days or years . . ."
The shield around the sun failed to contain it any longer and began to crack. The sounds of these fractures resonated across all of Equestria.
". . . Or less."
The sun violently exploded outward once it broke free from the shield's confinement.