Fractions of a second too small for a pony to appreciate them properly after Twilight had given the impulse, the first scale travelled from her back through the tube and shot out of the portion of the box on her leg. Together with it, delayed exactly so they would meet at the target, a magical bolt left her horn in the same direction, compelled by the box and willingly unopposed by her.
The two streaked through the air too fast to be anything but a blur to any observer. As Nightmare Moon unleashed a wave of energy towards the next giant projectile Starshine was hurling towards her and forced it to crumble to dust, the scale darted closer and so did the spell that would activate it. In the back of her mind Twilight hoped with all her heart it would work, though it all happened too fast for the thought to manifest.
That had always been the first backup plan. One she'd come up with quickly once forced to think of a solution to the problem of having to face Nightmare Moon in battle. Equestria's history was no stranger to exile as a tool against evil, and her contribution would likely be safer than most had been. There was nothing alive on the other side that Nightmare Moon would be able to hurt, and what was there was far more likely to hurt her instead. It would mean having to never use the scale again as a safety precaution, and having to worry about not ending up in that world by other means when travelling by equivalents, but all things considered those were minor inconveniences. Nightmare Moon did not know the spell necessary to traverse the scales, and any attempt at it would backfire on her tremendously.
That had been another considered option. Using scales as weapons by firing on them, and just letting them do as they did. Twilight had dismissed the approach, she did not wish to turn the Empire into a crater and certainly not when lives were there she would be taking. But she hadn't ignored the possibility completely, and other scales were ready, elsewhere, as a last measure. One she'd never activate herself, and she wouldn't be alive to see the activation of if it ever was used.
All those thoughts, memories and feelings, compressed, they flashed through her mind, unwinding as she finally took the shot and waited to see if it would work for a time so short she wasn't even consciously aware of her anticipation. The weapon Sunburst had created had come as a blessing. It would have been far, far more arduous to achieve the same effect without it, when scales could hardly be moved with magic without serious risks attached. Even if spells theoretically existed for it, warping the air around them to move that without properly touching the surface, they were never used. Even in the laboratory, scales were moved by hoof and wing, often not even their containers were enveloped in magic on the off-chance some leaked through.
The black box did not suffer from such issues. Whatever made it work, it wasn't magic. Whatever was going on inside it, something Twilight had no real knowledge of, it interacted with scales seamlessly. She'd reasoned it ought to have been the same power behind coils themselves, different from magic in the same way they were from it. But she'd known she would have time to think that over a different time, if she lived, and if not she would not be there to worry about it. First, what mattered was seeing things through in the first place.