What If Ash was in Pokemon Horizons?

A Great Battle! The Earth-Piercing Flame

The group wake up the next morning, arriving at the site Entei was last spotted after long hours of walking. Leaving most of the group with little energy to continue searching, except Ash, to no one's surprise. Everyone votes on staying at the site to have a small picnic to rest their legs, not knowing of those stalking them.

As the group finishes their food and packs up, they hear booming footsteps behind them. Finding the very Entei they're searching for walk up to them. Though it looks more primitive than the one they encountered in Johto.

"Is that Entei?" Roy asked, as everyone had frozen in stuuned slience for a moment too long for his liking.

 "It can't be, it looks way different than any Entei I've seen!" Ash commented with unease.

Pagogo began to stir in Liko's arms, calling out to Entei, before Lucius's other four Pokemon free themselves from their Poke Balls.

"Well, that proves it." Liko concluded, "This has to be Lucius's Entei."

Liko grabs Lucius's belt and walks up to Entei, holding it out to the Pokemon. "Entei, we've been trying to reunite all of Lucius's Pokemon and find Laqua. Will you please help us?" she asked, hope and fear in her eyes.

Entei responds by bringing out his own Ancient Poke Ball and placing it within the belt. Lowering the guard of the group. Thinking Entei was complying immediately, instead, the Pokemon snatches the belt and traps it under its foot.

"What's it doing?!" Liko panicked.

"It's challenging us!" Ash concluded, "If we want it to join us, we need to get the belt back first!"

Ash, Dot, Roy and Friede walk up to Liko and stand beside her, preparing for battle. Liko herself changes her stance, as Briar watches the fight with Pagogo from afar.

Entei secures the belt within its fur, and Roy starts with Stomping Tantrum with Crocalor due to Entei's weakness to Ground. Only for Entei to use Burning Bulwark to render the move useless.

Dot's Quaxwell follows up with Liquidation, but the attack fails and Quaxwell ends up burned from touching Entei. Ash sends out his Tauros, which shifts into an Aqua Breed upon using Surf, only for that move to not do as much damage as Ash had hoped.

"Okay, that's werid," Ash tensed up, "Surf should've done, like way more, right?"

Dot rubbed her chin, seeing the heat around Entei disappear, "I'm not sure," she started, "But I've got an idea. That new move Entei used, it must take up a lot of energy, so let's take advantge of that!" She proposed, causing Ash, Liko, Roy and Friede to nod.

Tauros, Crocalor, and Tauros bombard Entei with a combination of moves. Forcing it to use Burning Bulwark again, and the Pokemon maintain their distance until the move's effects wear off. Allowing an opening for Cap to jump in and fire off a point blank Thunder Punch, while Pikachu hits with Thunderbolt from afar.

Entei shakes off these moves, however. And retaliates with a powerful Dragon Pulse, shocking everyone.

"Since when can an Entei learn that move?!" Ash asked to no one, causing Briar to start searching her book.

"That's because It's probably not an Entei! It's a Paradox Pokemon!" Briar yelled, getting everyone's attention. "I don't know which one just yet, but I'll find out!"

"But that makes no sense!" Roy pointed out, "Rystal said it was an Entei!"

Briar didn't look up, "Well, Paradox Pokemon have only been recognised in recent years. So Rystal could have simply mistook it for an Entei, like we just did!"

Dot thinks for a moment, "Well, if it can use Dragon Pulse, and Surf and Liquidation didn;t weaken it.." She mused, "Then it's gotta be a Fire and Dragon Type!"

"Which means Stomping Tamtrum is our only good move." Friede added on.

Hearing this, Ash gets an idea, returning Tauros and sending out Hydrapple. Causing the others to give him confused looks. "Hydrapple knows Rollout, remember?" He said.

Floragato and Dot's Quaxwell still charge in with attacks, but the Paradox Pokemon doesn't use Burning Bulwark like they wanted. Cap sets up Double Team as a distraction while Dot's Quaxwell hides ina  nearby river, waiting for an opening to use Air Cutter. That opening arrives, and Quaxwell fires off the move, but instead of air being unleashed onto the Paradox Pokemon, it's water.

"Wait, that's not Air Cutter." Dot questioned.

"No, it's not! It's Aqua Cutter!" Ash exclaimed in excitement, his own Quaxwell escaping his Poke Ball to see the new sight.

The Paradox Pokemon gets fed up by the constant attacks, using Burning Bulwark again. Allowing Hyrapple and Crocalor to use their Ground Type moves to deal big damage. The Paradox Pokemon responds by shooting a Dragon Pulse into the sky, parting the clouds to give itself a ray of sunshine to boost its attack. Using Raging Fury as a threat of what's to come.

"Wow," Briar observed the new move, "That looks like a pillar of fire!" The something clicks within her, and she scrambles to a page in the Scarlet Book, "Everyone, I figured it out! This Pokemon is a Gouging Fire!"

Goging Fire unleashes another Raging Fury, this time firing directly at the six Pokemon against it. Causing Hydrapple to faint. The four kids look to each other and nod, it's time to end this. They Terstallize their Pokémon and attack from all directions. Quaxwell using a boosted Aqua Cutter to knock Gouging Fire into the river, leaving it wet and confused. Pikachu then lands the final blow: A Flying boosted Tera Blast. Knocking Lucius's belt out of it's fur, Floragto snatches it with her vine and swings it into Dot's hands. The battle's over, and they won.

Liko walks up to the Paradox Pokemon as the Terasatllization ends. "So, was that enough for you to join us?" She asked, the others watch with baited breath, Gouging Fire responds by sending everyone into another vision, showing Lucius himself struggling to tame Gouginf Fire, before he and Rystal fly off on Rayquaza.

As the group returns to reality, Gouging Fire walks next to Lucius's other four Pokemon. Pagogo also crawls near them. They cry in unison, their voices harmonizing as none other than the Black Rayquaza desends from the sky, looking down at our heroes.