I was going to leave the explanation for why Mimikyu is different than what we see in the anime for the "goodbye Pikachu" episode but since it seems so out of character for Mimikyu, here's a sneak peek:
"Pokespeech"
"hey look guys, it's the freak. We thought you weren't coming back until you become a Raichu."
Ash looked between Mimikyu and the rather large Raichu poking Mimikyu with its paw. "Are these your friends Mimikyu?"
"Boys, that's enough! Welcome home son. I missed you."
Ash didn't need to understand Pokespeech to understand the tears falling from Mimikyu's face as a Pikachu came from out of nowhere, hugging Mimikyu tightly.
"It's your mom isn't it?"
Ash was starting to wonder if it was going to be his curse to be constantly lost on his journey as he tried to make some sense of the map as he looked at a rather ominous looking bridge that definitely was not on said map.
"Brock, do you know anything about this area?"
"No, the farthest I've ever been is Mt. Moon."
Ash turned to Misty, who merely shook her head, "I've never been anywhere near here either."
"Does it seem odd to either one of you that this bridge is not on the map?"
"What other choice do we have?"
Ash thought for a moment, Misty did have a point, they did have to cross the bridge to get to their next destination, but that didn't mean they had to be silly about it.
"Pidgeotto, I choose you!"
Misty looked at Ash as if he'd grown a second head, until he had Pidgeotto land on the bridge, watching in disbelief as it crumbled under the bird's weight.
"A trap?" Brock questioned, "Who'd lay a trap like that out here?"
"Well we aren't going to find out just waiting around here are we? Pidgeotto, can you carry us across one at a time?"
Pidgeotto cawed at him, almost looking affronted as she picked up Misty with what looked to be very little effort. Slowly, they all made their way across the gorge.
"That was weird. We should keep an eye out for more traps just in case."
"Hey look guys, it's oddish." Misty pointed to what was indeed the grass pokemon innocently walking in front of them, "I'm going to catch it."
"Misty, I wouldn't" Ash tried to reason, "You don't know if he belongs to someone, and besides, aren't you a water pokemon master?"
Misty glared at Ash, who knew he'd said the wrong thing, "Yeah well I need some diversity in case I get someone using unconventional tactics again now don't I? Besides, I'll take good care of him."
Ash decided wisely not to say anything at all, merely following as Misty called Staryu to the field, but before she could call out a single attack a Bulbasaur came out of nowhere, pushing all three of them back with a razor leaf attack, causing them to stop near an old oak tree. Ash couldn't have been more surprised as they sprang yet another trap, this one a heavy net that dragged them up into the tree.
"I told you that you should leave that oddish alone. Whoever owns it must have set all these traps." Ash snapped at Misty
"Well, how was I supposed to know?" Misty snapped back
"Don't worry guys, I'll get us out of this if I can just reach..." Brock trailed off as Ash felt him reaching for something strapped to his ankle.
The net suddenly dropped, leaving no one any time to say anything.
"The next time we're in a net Brock," ash groaned from under Misty, "Don't cut it until we have something to fall on."
Eventually, the gang found themselves in front of a small cabin. The Bulbasaur from before saw them and growled as he took a defensive stance.
"You again?" Ash said, "Look, sorry about before, we didn't know that your friend belonged to anyone. Why don't you go get your trainer and we can explain."
"Look out Ash!" Brock pulled Ash out of the way just as the Bulbasaur tackled the spot where he'd been standing.
"Well all right then, if it's a battle you want."
"Hey! Just what do you think you are doing?"
Ash whirled around to see a beautiful young girl standing in the cabin's doorway, hands on her shapely hips.
"I'm sorry miss, but this Bulbasaur tried to tackle me before I could explain that we didn't know his oddish friend belonged to you."
The girl glanced at Bulbasaur, "What have I told you about battling trainers? Especially when it's for one of the Pokémon that has already left our care?"
Ash couldn't believe his eyes as the Bulbasaur hung it's head, "Hey, I'm sorry about before." Ash said, stooping down to Bulbasaurs level "We would never have tried to catch that Oddish if we knew that he was your friend. Truce?"
"Well, why don't you come inside, we can have tea and talk. My name's Melanie by the way."
"Ash."
"I'm sorry about Bulbasaur Ash, but all of my pokemon here are rescues. That Bulbasaur was abandoned by its trainer and ever since I took him in, he won't let any of the Pokémon get new trainers. It's sad really."
Ash eyed Bulbasaur, and once again he got down to his level, "Hey, I'm sorry about your trainer abandoning you. That must have been rough. But you have to know that we are different. Misty and Brock are both Gym leaders. They wouldn't be able to do that if they weren't trusted by the League and by their Pokémon. But I understand being protective of your friends too. I'm sorry again Bulbasaur."
As signaled to Brock and Misty that they should get going. Brock took one last longing look at Melanie but nodded. Just as they were heading out though Bulbasaur tackled Ash from behind.
"What's the matter Bulbasaur?"
"I think he wants a battle?"
"Well all right then!"
End chapter
you know how it ends from here. Ash catches Bulbasaur. took out Team Rocket because they aren't following Ash in this version.