What If Ash was in Pokemon Horizons?

The Approaching Shadow!

The trainers trek down Glaseado Mountain, Liko stares down at her feet. Her thoughts consumed by her recent loss against Grusha, and the fact she can;t use Terastallization anymore. They come across two paths, one continuing down the mountain, and one leading to the mountain's peak.

"Hey guys, why don't we see the top of the mountain?" Roy ased, "That might cheer Liko up."

"Great idea, Roy!" Ash praised.

"Do we have too?" Dot groaned, "I don't wanna go somewhere even colder.

"Well, we'll only go if Liko wants to." Roy explained.

They all turned to Liko, waiting for a response. "I actually think that would be nice." she spoke up.

"Then it's settled!" Ash declared, making Dot groan again.

The trainers head up the mountainside and exhaustion soon starts to set in, even for Ash. Roy spotted a cabin nearby, "There's a cabin." Roy panted, "Let's take a break."

"I'm good with that." Dot quickly said, eager to get out of the weather.

Roy and Dot begin walking towards the cabin, Ash is about to follow them, but stops when a giant boulder surronded by psychic energy moves in front of him, blocking the path. 

"Whoa, did you see that Liko?" Ash asked, turning to Liko. Only to find her absentmindedly walking in a different direction, too distracted by her thoughts to notice the boulder wasn't natural. Ash chases after her, yelling desperately, "Liko, wait! That's not the path Roy and Dot went down!"

Ash continues to follow Liko, calling desperately. "Liko, one loss against Grusha won't ruin your journey! Now, can you please look around and realize Roy and Dot aren't here?"

Liko finally perks up, looking back at Ash and then at her surrondings. "Oh, I guess we took a wrong turn."

"Yes!" Ash cheered breathlessly, "That's kinda what happened! Let's go back!"

Ash and Liko turn around, but before they can begin going back to reunit with Roy and Dot, they hear footsteps nearby.

"Maybe Dot and Roy found us." Ash suggested.

A figure comes around a tree, but it's not Roy or Dot. It's Amethio, Ash and Liko's eyes widen in shock, as does Amethio.

"You again." Amethio glared, "Hand over Terapagos before things get messy."

Amethio sends out Cerluegde, Ash and Liko won't back down though, Floragato and Pikachu take the field. Pikachu is suddenly taken by a spiderweb and is pulled up into the trees. Ash looks up to see a Spidops holding Pikachu hostage, Team Rocket dropping down from the trees.

"Surprise, twerp!" Jessie sneered, "Isn't Spidops amazing?"

Floragto growled at the old enemy, Ash simply groaned, "You guys again?! Can't you take a hint?"

"We'll be taking that as a compliment!" James said proudly.

James sends out his Capsakid to fend off against Ash. Ash sends out his Paldean Tauros as a counter, "Liko, you'll have to battle Amethio alone."

Liko nodded, "I'll do my best!"

Ash smiled, "Don't worry, you got this!"

Tauros glares down at the small Pokemon, yet it doesn't attack, still upset over losing to Tulip and having Nymble finish what it couldn't finish.

"You got this, Tauros!" Ash cheered, "I could have a hundred of you and you'd all be amazing!"

Tauros looks back to Ash and nods in repsect.  Tauros knocks out Capsakid with a quick Fire Blast, the attck burning up the spiderweb holding Pikachu. The little Pokemon scampers back up to Ash's shoulder, "Alright buddy, Thunderbolt!"

Pikachu unleashes the attack, only for Wobbuffet to protect the others with Counter.

"You're not getting rid of us that easily, twerp!" Jessie taunted.

Ash looks back to Liko, seeing Florgato taking a beating from a Terastallized Ceruledge. Before he can think about how to defeat two enemies, he hears another set of footsteps. Both battles come to a stop as Spinel casually reveals himself.

"Hello everyone." He greeted calmly.

"Gee, what's that guy doin' here?" Meowth asked.

"Why, I simply would like to preform a little examination." Spinel explained, pulling out a small test tube holding a pink shard.

"Wait, isn't that the Treasure of Eternity that Friede person was talking about?" Jessie asked.

Spinel smirked, "So you're familar? I'm very glad."

The tube releases a pink mist which Spinel's Umbreon inhales, causing it to cry out in pain and become completely feral, forcing Ash to remember a simlar event in Kalos involving a Zygarde Core and Team Leader.

"What are you doing to it?!" Ash demanded as Umbreon attacked every Pokemon with a strength no one had seen before.

Terapagos senses the Treasure of Eternity and forces itself out if its bag and starts angrily crying out at Spinel. Spinel simply smirks, "Is this little thing getting you all rilied up?" he asks, holding up the test tub as if to mock the little Pokemon.

"Stop it!" Liko exclaimed, trying to soothe Terapagos. The Pokemon wiggles out of Liko's arms and lets out a loud cry, transforming into its Terastal Form. Terapagos destroys the small shard with just one attack, returning Umbreon to normal.

Terapagos quickly returns back to normal and collaspes in Liko's arms. Spinel looks at the now empty container and smirks, "Thank you for your cooperation." was all he said before recalling Umbreon and running off.

"Hey, come back here!" Amethio chased after him, "What as that all about?!"

"We can't let them get away!" Liko cried.

"Right!" Ash recalled Tauros, "Looks like I'll have to blast you off another time." With that, Ash and Liko ran after Amethio.

"Oh, I am getting sick of the Twerp not taking us seriously!" Jessie growled.

"Well, I'm wondering that the Treasure of Eternity did." James pondered.

"C'mon their getting' away!" Meowth ran off, Jessie, Wobbuffet and James running after him.

The trainers eventually corner Spinel in a cave, where he mysterious disappears as if he were a Psychic-type Pokemon. "Where'd he go?!" Ash demanded.

Amethio hears a faint sound, he turns around to see a gaint rock being carried with psychic energy being place in front of the cave's entrance. "It's a trap!" he exclaimed.

The trainers quickly rush back towards the outside, trying to escape before the rock blocked them in, but the rock was quickly placed directly in their path. Forcing them into nothing but darkness and cramped space with no sign of escape.