Stella smirked at that, and sent the sphere flying up next to the castle, Sunburst inside it looking with worry at Starlight and trying to understand what was happening to her. "Now, then. About that. Shall we beg-"
She didn't finish her sentence. She found herself blocking a spell fired by Twilight's horn, a stream of magic taller and wider than a train aimed straight at her and fired from such close range she had barely seen it coming. Holding it off was not an issue, but being cut off so abruptly still did irk her. She would have snarked back at Twilight, but she was aware the other wouldn't be able to hear her. Instead she focused on pushing back against the spell.
Then a few things happened in quick succession. A bolt of lightning came down from the clear skies, aimed at Stella's flank. In the split second she took to feel it coming in time and use her magic to defend herself, Twilight's spell stopped flowing from her horn. Between the moment the last of it left her body and the moment that reached Stella, whose vision was still hidden by the flow, Twilight readied up and cast another spell. It all happened so fast those watching caught almost nothing of it, pieces at most, and by the end the only thing they all observed was the final result of Twilight's last spell. Both alicorns were gone, and a few others of the ponies there were too.
Stella cushioned the fall that followed her reappearance with a blast all around her that left a glassy crater into the sand and dry dirt of the soil below her. From behind her shield Twilight said in tones that felt mocking, "I figured we should make sure no one else would get hurt, or accidentally interfere."
"You cheated," Stella growled, firing a stream of magic and spells and bolts at Twilight that the other alicorn only narrowly avoided or shielded herself against through quick flying maneuvers, barriers and teleportation.
"Yes," Twilight said, her voice magically amplified to be heard above the cacophony of Stella's blast hitting the ground past her and dotting the landscape in craters. "On your left!"
There was a blast at Stella's right, sudden and unannounced, and it sent the alicorn tumbling and sailing through the air. She recomposed herself quickly and teleported.
She appeared on top of Twilight, and the two locked horns, the air around them distorted and singing out like metal sheets being bent and torn apart, portions of it glowing white hot as their raw magic powers clashed. "Don't think this is going to help you." Stella was angry, fire in her eyes.
Twilight was almost smirking, though looking a little fatigued. "Talk less."
Lightning came down again, striking where Stella was. It crashed around the sphere of energy surrounding her, and the bolts that followed did the same. Twilight swallowed nervously as Stella's eyes began to glow. Then the latter's magic flared.