Twilight glared at her opponent.
She had been just setting down to sleep after a long day of researching indigenous cactus species when the she heard a feral howl and caught a dark shape moving in her peripheral vision. She thanked the creator that she had pestered her brother Shining Armor to teach her how to defend herself. That training now all came back to her as a small round shield snapped into place in a fraction of a second, thus saving her from being gutted by claws larger than her hoof. Her instincts, well honed by days of instruction at her brother's hooves served her well yet again as she rolled away from the beast and snapped up a more omni-directional dome shield which was impacted by another clawed limb from behind her, right were her blind spot would have been had she stood still. The initial two attackers had been joined by three others and ever since then the wild beasts of the Wastelands has been making a disjointed effort to get at her.
Twilight let lose an explosive gust of a sigh as she checked the position of the moon. "Only a few more hours until sunrise," she thought aloud. Whether the beasts understood her or were simply enraged by her tone of voice, they all growled and renewed their attacks. Twilight winced with every impact. Brilliant as she was at calculation magical force equations, she had quickly come to the conclusion that, despite her large reserves, constantly refreshing one shield to it's full strength would drain her too quickly. She had thus used the Wayfinder type 5 shield (variant 2), which consisted of many small hex shaped shields layered on top of each other. It was said that Shieldmaster Wayfinder himself came up with the concept after observing the way a dragon's scales moved over top of each-other.
The idea was that rather spreading the damage across the entire shield and then constantly refreshing the whole thing, one could simply refresh a smaller section of hexes while still keeping the maximum strength in the ones that didn't get hit. The second variant used a concept called "ablation" which called for disposable hexes. Rather than constantly refreshing the outer layer of hexes, the caster would simply expand out the layers of hexes and cast a new layer inside. In this manner much energy could be conserved. The only reason it wasn't used in all battlefield situations was that it required incredible control and discipline to pull off (something she had in spades).
A little known fact about shields was that although they were indeed solid, they had no mass, and thus didn't require the caster to expend energy to keep them in one place. Indeed it took a more complex spell to make a shield that followed the caster around. This was why her brother could refresh the shield around Canterlot during his wedding from anywhere in the city. Thus, Twilight did not have to worry about her shield moving as she flopped to the dusty ground with a huff and closed her eyes.
Think Twilight Think! Even at the much reduced energy cost of variant 2 you still won't have enough. Glancing up at the softly shimmering hexes she remarked to no-pony in particular that the moon looked quite beautiful tonight, even through the distortion of the shields many layers. Speaking of which... She hoisted herself to her hooves and passed a hoof over the many smaller hexes on the inside of the shield, making sure that there were no defects. She could have used a simple spell to check them, but that would use up energy that could go into more hexes. A manual inspection would have to do. As she was scrutinizing one particular patch she ran her hoof over another and quickly recoiled in pain. Glancing down she had actually cut herself on one of the hexes.
Sloppy work Twilight. You made the edges too thin. And you managed to injure yourself. Horray. Looking down at her only injury of the night, she paused. It couldn't possibly be that simple. Quickly running through everything she knew about shields and magical constructs (which was quite a lot) she desperately thought up a plan. The beasts wouldn't keep circling her shield forever, soon they would be back on the offensive. Magical constructs hold their position in real-space relative to their caster's initial position unless otherwise stated in the construction matrix. Could it work? As a test, she created another hex of moderate size, free floating vertically inside her shield, this time with deliberately thin edges, as thin as she could make them and still keep integrity. She pulled out a lavender hair from her mane and draped it over the edge. Or rather she would have if its own weight hadn't caused the hair to be sliced in half. That's...really sharp. Her theory proved, she ran through some mental calculations and found the best design. Then she double checked those calculations and triple checked those calculations. When her standards of perfection had been met, she gave a determined look to the beasts outside the shield.
She would have to sacrifice her static shield and make a new one inside that would move with her, but it was a small price to pay. She quickly expanded out her current shield and made a dome shield one inside it. This one would move with her. Then she created layers of diamond shaped "scales" on the outer edge of her dome. The beasts stopped their relentless pacing to observe her new move with confusion. Then she got a grin. A terrible, malicious grin. The kind of grin that she had seen the Princess use on court nobles as she led them around by the nose in a verbal debate. The grin that said "I am so far ahead of you that I've already won and you just don't know it yet." In a flash she willed the scales to all stand on end so so that their flat sides rested against her dome. She then started spinning them. One ring widdershins, the next anti-widdershins, the next the same as the first, so on and so forth. They let off a high pitched whine that she could only relate to thousands of tiny swords swiping through the air all at the same time. She had gotten the inspiration from the teeth of a saw, but now in this context it took on a much more dangerous use than cutting wood. If the weight of a hair cut through with no resistance, what would the spinning force on top of the force of a charging beast do? She found out quickly when one of them tried to lunge and swipe at the source of the high pitched whine and one of the claws on it's limb went spiraling off into the distance. The best let loose a howl and dashed away from her, quickly followed by its brethren.
The beasts of the Wastelands ran as fast as they could, desperate to escape from The Pony That Whined.