"What if someone sees," Hermione said fearfully. "Umbridge doesn't want us to learn Defence Against the Dark Arts, because she's convinced herself that Dumbledore wants to use us as his private army! The last thing we need is people seeing us!"
Unfortunately for her, nobody was listening to her; Fred and George had flattened the field's tall grass in the shape of a long rectangle and positioned Oleandra and Harry at the opposing ends. The two duellists both knew proper duelling etiquette, thanks to their brief stint with Lockhart's Duelling Club, so they bowed to each other.
Oleandra decided not to make use of Fairy Magic during the duel; it's not as if its use could be detected, but she wanted the duel to be fair.
"Alright, let's have a good, clean fight!" said Fred cheerfully. "No kicking, scratching, no biting— if you can help it. Now, on the count of three— one, two…"
"Two and a half," said George.
"Three!"
"Expelliarmus!" shouted Harry immediately, pointing his wand at Oleandra in a flash.
Harry was fast, and he had good reflexes. He was also intimately familiar with the Disarming Charm. Not just anyone could have parried or dodged his sudden attack while concentrating on their own attack.
However, Oleandra was much more experienced than Harry when it came to life-and-death magical fights, and she had also learned a new trick while learning the way of the sword under the Sorting Hat.
(Literally, as it needed to be on her head if they were to talk to each other)
With her Mystic Eyes, Oleandra could actually see Harry drawing magic into his body, focusing it through his wand, and releasing it. Timing, vector, she could guess it all, much like she could determine a Bludger's trajectory.
Unlike a Dragon, which would produce its own ancient magic and accumulate it throughout its body, Wizards constantly absorbed magic from their environment and expelled it from their bodies. It was a lot like breathing; except it was magic instead of air; Magical Circuits instead of the lungs, heart, and blood vessels.
As such, a Wizard would never run out of magic, because magic was everywhere around them.
Right before Harry fired his spell, Oleandra leaned to the side slightly, causing Harry's spell to miss before he had even released it. And at the same time that he was finishing chanting his spell, Oleandra was also finishing hers:
"Legilimens!" Oleandra chanted loudly and clearly.
Last year, Harry had resisted the Imperius Curse with much greater ease than his fellow students, so it stood to reason that he would exhibit similar defences against a spell of the same discipline. But to Oleandra's surprise, penetrating Harry's mental defences turned out to be much easier than she had thought it would be.
Even now, she could feel question marks popping up over his head: he didn't know this spell. Legilimency didn't produce any light shows or sound effects, so he was wondering if her spell had failed, or if it had worked, but he hadn't noticed it yet.
Upon seeing Oleandra take a step forward, Harry raised his wand. He was going to use the Impediment Charm to stop her from closing the gap.
"Impedimenta!" he cried.
"Finite!"
Oleandra decided to be fancy and cancel out his spell the instant it hit her. Harry's spell did not slow her for even a single second; Oleandra had timed her Counter-Spell too well.
"Harry, she's reading your mind!" Hermione screamed shrilly.
If Harry was unnerved before, he definitely was panicking now. All he could think about now was…
"Protego!"
…The Shield Charm. Since she had Elhaz, Oleandra had never bothered to learn this particular spell, so in this duel, she absolutely had to avoid getting hit by dangerous spells.
Unfortunately for Harry, Oleandra had already established a connection between their minds, so the Shield Charm wouldn't dispel her magic. It would have been different if he had cast it directly in response to her Legilimency attempt a few seconds ago, but it was too late now. With Oleandra's level of proficiency, Harry only needed to break eye contact in order to cancel the spell, but he didn't know that yet.
…Hang on, if their minds were connected, didn't that mean that she had effectively lowered her own runic mental defences in order to use Legilimency? She was completely vulnerable to mental magic right now!
"Ducklifors!" Oleandra sang, pointing her wand at a wooden fence. "Go, my ducks! Flush him out from behind his shield!"
With a poof, the fence turned into two dozen ducks, which Oleandra directed to attack Harry, hoping to make him drop his magical ward. The ducks flew at him as one, pinching at his clothes and his skin with their round beaks, causing him to lose focus.
"Flipendo!" Oleandra called out.
But unfortunately, her Knockback Jinx hit one of her own ducks by chance, causing her Transfiguration spell to end in advance. The ducks turned back into pieces of wood, which came tumbling down on Harry's head, probably inflicting more damage on him in this form than they would have if they had remained as birds.
She could still read Harry like an open book; he had had enough, so he was going to attempt to Stun her next; three shots left, right and centre, making it impossible for her to dodge, unless she…
"Stupefy! Stupefy! Stupefy!"
Oleandra ran to the side and jumped, twisting her body in the air as she performed a free cartwheel; an aerial cartwheel during which one's hands didn't touch the ground, that is. The crowd oohed and aahed upon seeing the three crimson Stunners fly past her limbs, coming rather close to grazing her…
Oleandra knew the Sorting Hat had warned her not to attempt this kind of stunt in combat, but where was the harm in doing flips during a friendly duel?
She could dodge like that without breaking a sweat, but she knew she couldn't end this fight, since she didn't know any neutralizing spells that didn't involve runes. Daphne probably knew the Stunning Spell, but Oleandra had never used it herself…
"You can do it, Oleandra!" Tracey cheered from the sidelines.
Oleandra turned around and waved at her cheerily.
"Expelliarmus!" Harry shouted.
Professor Moody wouldn't have been proud, but it was Oleandra's own fault for turning her back on her opponent!
"Aguamenti!"
Oleandra lazily dodged without looking and fired a high-pressure blast of water from her wand at Harry, using the Water-Making Charm.
"Stupefy!" Harry managed to cry before getting hit with the jet of water. "Oof!"
Incidentally, magic was extremely similar to light, in that it obeyed the three laws of reflection when it travelled. Indeed, upon hitting a reflective surface, a spell's magical beam would be reflected with the same angle as its angle of incidence. And magic could also be refracted if it travelled through different media…
It was a one in a million, but Oleandra was anything but a lucky girl.
Harry's Stunner completely missed her, striking instead the jet of water that was gushing out of Oleandra's wand. Then, Oleandra's magical water redirected Harry's Stunner— his spell had struck her jet of water at the exact critical angle needed in order for it to be refracted parallel to the stream of water!
Oleandra had effectively put Harry's spell on guided rails towards her, so his Stunner travelled along the entire length of the column of water spouting from her wand…
…and hit her squarely in the chest.