Once the dust settled, it was agreed that – depending on the definition you use – Starly, Rayquaza and the youngest of the Spiritmob all had a claim to be Ash's youngest Pokémon on the grounds that pinpointing Starly's actual date of birth was too difficult to rule him or Rayquaza out.
With Mew already locked in as the oldest, Byron just shrugged and said that he'd do a four Pokémon per trainer battle instead… but that that did mean that the Pokémon being used had to be chosen randomly.
"How do we do that?" Ash asked.
In reply, Byron wrote something on each of four slips of paper, then put them all in a miner's helmet.
"Like this," he said, taking out a slip and concealing it. "Now you do it."
Random selection done, the first Pokémon Byron sent out was a big Bastiodon.
"Oh, I worked with one of those at the Summer Academy!" Ash said. "And my friend Gary was protecting some Shieldon a while ago… is Bastiodon a Pokémon who got revived or were they born in this time?"
"He's first-generation," Byron replied. "A direct fossil revival."
"So I guess in one way he's your oldest Pokémon," Ash considered. "But not your starter, then…"
Then Ash sent out his Pokémon, which turned out to be Mew.
"Hiya!" the Psychic-type giggled. "Hey, want to see a cool trick?"
"That depends," Bastiodon replied. "Is it going to hurt?"
"Oh, um, actually it might," Mew admitted. "Still, this is a battle! Is it a battle? I haven't heard anyone say start yet."
Byron decided that that was a good moment to start the battle. "Begin! Flash Cannon!"
Mew zipped to the side, avoiding the blast of silver light, and tapped his chin. "I think that's a yes!"
With a pop and a flash of white light, he turned into a little red-and-black lizard.
"Toxic-to-the-face!" he said, hitting Bastiodon with a glob of purple poison.
"Steel types are among the most defensive Pokémon in the world," Byron said. "And they're specifically immune to… wait."
He frowned. "Bastiodon, are you turning purple?"
"Am I poisoned?" Bastiodon asked. "It stings."
"Yep!" Mew agreed, reverting from being a Salandit. "I thought it might be interesting for you to experience it… plus, it is a battle, like I said!"
"Bastiodon, Flamethrower!" Byron ordered.
"Mew, fight fossil with fossil!" Ash suggested. "Dracozolt time!"
"That's a great idea!" Mew agreed, avoiding the Flamethrower blast and turning into Dracozolt.
Byron did a double-take. "What fossil Pokémon is that? It looks like two halves of different Pokémon…"
"Original chimera, do not steal!" Dracozolt said quickly.
"Bolt Beak!" Ash called. "Then use Earthquake!"
"Iron Defence!" Byron ordered quickly. "And – Avalanche!"
The ground shook and a blast of snow hit Dracozolt, who spluttered and slid backwards slightly on the now-frozen floor. "Ack! Pth! Snow is bad for Dracozolts!"
"Aura Sphere!" Ash said. "Then use Thunderous Kick!"
"Hiii-yah!" Dracozolt called out, avoiding the second Avalanche attack more successfully and hitting Bastiodon hard enough to make a klannng noise that reverberated through the building.
"Metal Burst!" Byron said, prompting Bastiodon to release a blast of sound that returned much of the force of the Thunderous Kick attack.
"Meteor Assault!" Ash said.
Dracozolt hit Bastiodon with their thick leek.
Not actually having a leek didn't seem to present an obstacle.
"Well, that went… about as well as I could have hoped, honestly," Byron admitted, returning Bastiodon and switching to the next Pokéball. "Let's move on so I can stop focusing too much on how ridiculously hard to beat that Mew is."
"I'm a massive challenge!" Mew said proudly. "My greatest strength is versatility. Still haven't worked out how Pikachu does the Earth Breaker thing though."
"The what?" Byron said.
"Don't worry about it," Ash advised. "My second Pokémon's ready!"
He held up the Pokéball as proof, and Byron sent out a Bronzor.
Ash's Pokémon was Starly, but even as he came out Bronzor evolved into Bronzong.
"Huh!" Ash said. "It's been longer than I was expecting since a Pokémon evolved in the middle of a Gym Battle."
"The battle hasn't even started yet," Byron protested.
"Yeah, that's in the middle as far as I'm concerned," Ash replied.
"In which case… begin," Byron said. "Bronzor – Bronzong – use Extrasensory!"
"Left!" Ash called, as Bronzong tolled and let out a pulse of psychic energy, and Starly flitted to the side in a blur of wings. The attack whipped past, missing, and Starly glanced at Ash for guidance.
"Bronzong might have Heatproof or Levitate," Ash told him. "So use Dark Pulse!"
Byron frowned, and Starly flicked his wing out to send a pulse of fizzing purple-black energy towards Bronzong.
"Gyro Ball!" the Gym Leader said, and while Bronzong had only just started to spin up when the order came it was moving fast enough to avoid the worst of the attack.
"Force Palm!" Ash decided. "It's still going to be kind of effective – then follow it up with Bone Rush! See which Ability Bronzong has!"
"Spin up faster!" Byron replied.
The first strike by Starly saw the Flying-type knocked away by Bronzong's arms, and he flipped once before recovering and flinging a pair of Bone Rush bones at Bronzong. They hit with a double klang sound, still mostly deflected by the ongoing Gyro Ball.
"Then… let's try something else!" Ash decided. "Fly directly overhead! On top of Bronzong!"
"Extrasensory," Byron countered, and Bronzong sent out another pulse of gold-orange psychic light. It flashed up towards Starly and half-hit half-missed, knocking Starly about a bit but mostly wasting its energy.
"Now, Aura Sphere!" Ash said. "Spin it the other way to the way Bronzong is rotating! And follow it down, then use Strength!"
"What are you-" Byron began, then overrode himself. "Look out, Bronzong! Keep that spin going!"
Bronzong was not able to keep the spin going. Starly's Aura Sphere robbed a little too much of their rotational speed, then the Flying-type himself grabbed on to one of Bronzong's ringer arms and used Strength – lifting Bronzong up into the air, then flipping it around to crash the Steel-type into the ground.
"How exactly is that even possible for such a little bird?" Byron demanded. "I know you said to use Strength, but the question remains!"
"He's being taught by a Lucario," Ash shrugged. "At that point I think you don't really have to worry about size, even if it did count with Pokémon."
Byron's third Pokémon, once Bronzong had been removed from the crater in the floor and they'd shifted to the other side of the big main room, was a Skarmory.
By way of reply, Ash sent out Yveltal.
"...what," Byron said, not really phrasing it as a question.
"One of the Magneton clusters in the Spiritmob has a really, really good memory," Ash explained. "So I checked with them, and they agreed that Yveltal was spirit number one hundred and eight out of one hundred and eight, which makes him the youngest of the Spiritmob!"
"I'm kind of gratified that you've started calling them that," Ho-Oh said, from where he formed part of the massive panel of spectators.
"It's clever," Ash explained. "Anyway, let's get on with the battle!"
"Do we have to?" Skarmory checked. "It's all well and good for me to go out there and do my best to win a battle, and I don't mind trying if my trainer insists, but this is Yveltal! The Legendary Pokémon of Death, even if this particular one is a younger version rather than the original one. I mean… does being Sturdy even help in this situation?"
"I actually don't know the answer to that question," Yveltal confessed. "But if there is any comfort, Ash knows a Xerneas who is not formally his Pokémon but who lives near his home. So there is literally nothing I could do to you that could not be wholly reversed on an outpatient basis."
"Or I could-" Ho-Oh began.
"No, father," Suicune said, not unkindly. "While the sentiment is appreciated, and we all know you want to help, I do not think that Byron or Skarmory would appreciate his ending up as a Magearna or something along those lines."
"...at least he would still be Steel type," Ho-Oh said, softly. "I am almost seventy percent sure I would get that right."
"Nevertheless," Suicune replied.
"All right, fine," Ho-Oh sighed. "You win. I will leave any resurrections required to one or more Xerneas."
"I should probably say something about how casually you're talking about this," Byron said. "But then I remembered that I revive fossils a lot. So that's kind of similar."
"Actually, how do you do that?" Yveltal inquired. "Because Oblivion Wing at full power turns things to stone, and apparently you can turn stone into living Pokémon? It sounds related."
"Maybe we can talk about it later," Byron suggested. "Right now, the main thing I want to do is-"
"Ooh, actually, how much of a Pokémon do you need to have to revive it?" Mew interrupted. "I've met revived Archeops before. If you can revive a Pokémon from a feather, and an Archen lost a feather that got fossilized but the Archen lived to today, couldn't you have an Archen revived from the feather next to the Archen who donated it?"
"Begin," Byron said, firmly. "Rock Slide."
"Surprise him, Yveltal!" Ash replied, as the Dark-type rolled out of the way of the attack.
Skarmory's wings rattled as he looked around, alert for what the surprise could be.
"You using Oblivion Wing wouldn't be very surprising," he said, hopefully.
In reply, Yveltal vanished.
Then a shadowy wing appeared from the floor, grabbed onto Skarmory's foot, and began slamming the Steel-type against the walls, floor and ceiling.
"I'm not sure that that's how Phantom Force is meant to work," Pikachu said, as Yveltal landed again.
"Well, it was certainly Phantom," Yveltal replied. "And it involved a lot of force. So it seems to fit."
Pikachu chuckled. "Yeah, that's fair."
"Well…" Byron began, then stopped and tried again. "I'm going to have to do something nice for Skarmory about that one."
He got out his last Pokéball. "Steelix, are you sure you're all right battling Ash's last Pokémon?"
Steelix came out of her Pokéball in response.
"I'm ready," she said. "I know that whatever it is is going to be tough, but I don't mind handling it."
Rayquaza uncurled from under Ash's jacket, and waved.
"Hello," she said, nodding her upper body in a bow. "My name is Rayquaza. It's nice to meet you."
Steelix tilted her head.
"I'd have expected you to be longer," she confessed. "And green."
"I can't believe I'm saying this," Byron admitted. "But I know we went over the Pokémon that Ash has back when he won the last League he took part in. Including that his Rayquaza is both small and shiny."
"In fairness, that was a long time ago," Steelix said. "Anyway, I'm Steelix."
"Oh, are Pokémon allowed to Mega Evolve and things like that in this battle?" Ash asked.
"Why not," Byron decided. "Mega Evolution is a sign of trust and a bond between trainer and Pokémon, and also Steelix and I can do it. So I'll allow it."
Steelix took a deep breath, and Mega Evolved.
Rayquaza got the Red Orb out of her backpack, and turned into Tiny Shiny Primal Groudon.
"I should have known it would be one of these days," Byron admitted. "Do your best, Steelix!"
Mega Steelix did her best.
This turned out to not quite be sufficient to a Pokémon who – simply by existing – had had a significant effect on the local climate, and who also knew Precipice Blades.
On the plus side, the hole in Canalave Gym wasn't that big, and it did mean they got to meet the various Fossil Pokémon who lived in the gym. And Mew told everyone to please stand back because she was about to do magic science, then took a deep breath and used Roar of Time to revert the gym to the state it had been before it got damaged.
Plus, Ash got the Mine Badge. Which had been the point of the whole endeavour anyway.
AN:
Really, he should have known it was one of those days yesterday.