Old Faces, New Phases?

Ash, Lillie, and Ilima strolled their way to Verdant Cavern, presently resting in a small town on the way.
"This place is called Pua Town. Verdant Cavern isn't too far from here, another hour of walking at most."
"Sweet! We'll rest here for the night and make way for my first trial tomorrow."
Lillie looked around, taking note of the oddly clean streets.
"Gee this place sure is clean. There's not even a wrapper lying on the streets. I wonder how they keep them so clean?"
Ash and Ilima scratched their heads, not having an answer to her question.
"Hey guys!"
Everyone turned to see Sun running up to them, an unknown girl following close behind him.
"Sun, how's it going?"
"Great, just stopping by my hometown for some training."
"Ahem."
Sun laughed as his companion tapped her foot impatiently.
"He he, right. Guys, this is my little sister Moon. She'll be starting her adventure in a month."
"Nice to meet you, Moon."
Moon's expression brightened.
"You too. My stepbrother here has told me about you guys. Hey, big bro, isn't that pink haired guy the one who creamed you and Hau-"
Moon was cut off by Sun clamping his hand over her mouth, laughing nervously as whatever she was going to say next got muffled.
"Now now, no need to live in the past."
"Hey Sun, how do you guys keep the streets so clean? Even back in Pallet Town there's usually some litter lying around."
Sun chuckled lightly.
"Well, its nothing really. See, we have Grimer and Muk to thank for that. Moon?"
Moon stepped forward, continuing the explanation.
"You see, Grimer and Muk live off of eating Garbage mainly, so in exchange for keeping the streets of Alola clean, we keep their homes well kept. Its
kind of a win-win situation."
To illustrate their point, a Grimer came shuffling down the street and, noticing a discarded food wrapper, eagerly gobbled it up before continuing on his way. However, Ash was quite surprised by its appearance.
"Guys, call Nurse Joy quick! That Grimer is ill! Just look at its miscoloration."
Indeed, the Grimer did look very different. Instead of its normal Purple color, its body was a lime green with a yellow ring around the mouth. Everyone stared at him in confusion before it dawned on them, Sun being the first to speak up.
"Oh, you're from Kanto, right?"
"Yeah."
"Well Ash, some Pokémon who have migrated from Kanto aren't used to the Alolan climate. Therefore, their bodies undergo changes to better adapt to their new environments."
Moon stepped forward to continue the explanation.
"You see, these changes can be as simple as becoming a dual type Pokémon to completely changing their type altogether. For example, Alolan Grimer and Muk are Poison and Dark Types."
"Woah, that's awesome!"
Then Sun had an awesome idea.
"Hey Ash, would you like to have a Pokémon "battle? I've caught some new Pokémon that you might find interesting."
"You bet! I cant wait to see all of the new Pokémon you've caught. Ilima, would you mind referring?"
"Of course, Ash."
"Two on two sound good to you?"
"You're on!"
After finding a good sized clearing, Ash and Sun stood a good sized distance from each other, Ilima and the spectators off to the side.
"This Pokémon battle between Ash of Pallet Town and Sun from Pua Town shall begin. Each trainer shall use three Pokémon each, no substitutions. Sun shall make the first move. Are you ready?"
"I'm ready when you are, Ash!"
"All systems are a go!"
"Then let the battle commence!"
"Go, Meowth!"
"Litten take the stage!"
Ash and Sun sent out their first Pokémon. Ash was surprised to see a dark grey colored Meowth instead of the usual tan colored kind.
"Woah, is that another Alolan form?"
"Yep, this one's a dark type. Pretty cool, huh?"
Moon pouted from the sidelines.
"Ah, I wanted to take Meowth on my journey! Stupid Paper, how does it cover Rock?"
Sun laughed nervously, but continued. Meowth, on the other hand, took one look at Litten and yawned, hardly impressed. This made Litten growl in anger.
"Meowth, use Quick Attack!"
"Flamethrower, Litten!"
Meowth sprinted toward his target, ready to pounce when Litten let loose a large burst of flame, singing Meowth and pushing him back.
"Litten, use Lick!"
Litten ran up to its opponent, giving it a hard lick from the top down. Although it wasn't very effective, being a ghost type move against a Dark Type, it was enough to paralyze it.
"Shake it off Meowth and use Pay Day!"
"Scratch, Litten!"
Unfortunately for Sun, Meowth was fully paralyzed, leaving it vulnerable to Litten's attacks as it relentlessly assaulted it with its claws. By the time Meowth could move again, it could only collapse in exhaustion, unable to continue any further.
"Meowth is unable to battle! Litten is the winner!"
"Way to go, Litten!"
"You did good, Meowth. Now take a good long rest."
Litten purred proudly as Meowth returned to his Pokeball. Suddenly, he started to glow, to everyone's surprise.
"Woah, Litten is evolving!"
When the glowing stopped, Litten had become larger, with the orange on its body becoming more prominent.
"Torr, Torracat!"
Rotom buzzed to life, flying out of Ash's pocket and scanning the new Pokémon.
"Zzzzt, woah a new Pokémon! Torracat, the Fire Cat Pokémon, and the evolved form of Litten. When its mane is standing on end, you can tell its feeling good. When it isn't feeling good, its fur will lie down flat."
"Way to go, Torracat! I knew you could do it."
"Pika Pi!"
Torracat smiled, rubbing up against its master's leg and purring softly. Sun smiled confidently.
"Good, now it'll be an even match. Go, Brionne!"
From the Poke Ball emerged an elegant looking seal, doing a cute dance before posing for battle. Once more, Rotom scanned the new Pokémon."
"Zzzt, Brionne, the Pop Star Pokémon, and the evolved form of Popplio. A skillful dancer, it creates a sequence of water balloons as it dances, and briskly bombards it's enemies."
"Woah, I guess your Popplio evolved, huh?"
"Yep, and we're ready to rock this battle, right Brionne?"
"Brionne!"
"Alright, Torracat, use Fire Fang!"
"Water Gun, Brionne!"
Torracat leapt forward, teeth a blaze and ready to bite. Brionne was ready, though, and sent out a burst of water, pushing Torracat back.
"Double Kick, Torracat!"
"Aqua Jet, Brionne!"
Torracat shook off the water from his fur, ready to fight back, but Brionne was too fast, slamming right into it with a burst of water. Tired and unable to continue, Torracat collapsed where he stood.
"Torracat is unable to battle! Brionne is the winner!"
"Awesome job, Brionne!"
"Bri!"
"You did a good job, Torracat. Get some rest."
After returning the weary Torracat to his Poke Ball, Ash turned to his starter.
"You ready, Pikachu?"
"Pika!"
Pumped up and ready to battle, Pikachu leapt onto the battle field, sparks flying from its cheeks.
"Battle begin!"
"Pikachu, Volt Tackle!"
"Aqua Jet, Brionne!"
The two Pokémon met in the middle, Pikachu in an aura of electricity and Brionne in a veil of water. A small explosion occurred pushing them both back.
"Pikachu, Quick Attack!"
"You too, Brionne!"
Once more the two clashed, Brionne being slightly faster but only just. Once more the two were pushed back, tired but neither one ready to back down.
"Pikachu, Thunderbolt!"
"Water Gun, Brionne!"
"Pikachuuuuuuuuuuuuu!"
"Brioooooooooooooone!"
For the third time their attacks clashed, Pikachu's electric bolts versus Brionne's Water burst. Finally, a huge explosion erupted, enveloping the battlefield in smoke.
When it finally died down, Pikachu and Brionne were revealed, both out cold.
"Both Brionne and Pikachu are unable to battle! This match ends in a draw!"
Nodding to each other in approval, both Sun and Ash recalled their Pokémon, Sun by returning it to its Poke Ball and Ash by picking Pikachu up."
"You did good, buddy."
"You too, Brionne."
"Pika."
Ash and Sun met in the middle and shook hands.
"That was a great battle, Sun. Your Pokemon are amazing!"
"Hey, you're pretty good yourself. Brionne and I need to practice some more."
With that the two went their separate ways, Sun and Moon heading for home while Ash and his gang headed for the Pokémon center.
"Ash, have you chosen which Pokémon you'll use for your upcoming Trial?"
"Yes, making a good choice can be the difference between Pass or fail."
Ash smiled knowingly.
"I do, but first I need to make a phone call."