Evolution by Fire! (Japanese: 炎のメモリー！ポカブVSエンブオー！！Flaming Memories! Pokabu VS Enbuoh!!) is the 77th episode of the Best Wishes series, and the 734th episode of the Pokémon anime. It first aired in Japan on May 3, 2012 and in the United States on September 1, 2012.
On their way to the Icirrus City Gym, Ash, Iris, and Cilan decide to spend the night at the Pokémon Battle Club in Astilbe Town. There they witness a Double Battle between two Trainers: Shamus, with his “Fire Warriors” Heatmor and Emboar, quickly defeats Kylan, with his Mienshao and Watchog.
At dinner, Tepig seems to recognize Shamus and goes bounding up to him. Iris reminds Ash how he and Tepig met after it was abandoned by its Trainer in Accumula Town—and based on Tepig’s reactions, it appears Shamus was that Trainer! Ash and Iris are furious and demand an apology for how he treated Tepig, but Shamus insists he left Tepig behind for its own good because it was too weak to battle.
Don George suggests that Ash and Shamus resolve their differences with a Double Battle. Shamus plans to use his Fire Warriors, and Snivy—who also had problems with its original Trainer—volunteers to be Tepig’s partner for the battle. But Tepig is reluctant to battle against Shamus, remembering how they parted in tears.
As the battle unfolds, Shamus reveals that he was faking his emotional goodbye so Tepig wouldn’t follow him! Tepig is utterly destroyed by this, and despite the type disadvantage, Snivy bravely steps up to take on the Fire Warriors all by itself. Inspired by its friend’s courage, Tepig resolves to prove its strength—and then evolves into Pignite!
The battle really heats up, and Pignite quickly shows that Shamus underestimated it, taking down the Fire Warriors by itself. Defeated, Shamus finally apologizes to Pignite and tries to convince it to rejoin his team—but Pignite sends him on his way with a fiery refusal, and our heroes are off to Icirrus City once more!
After their adventures in Twist Mountain, Ash and his friends decide to stay at Don George's Battle Club in Astilbe Town for the night. Before reaching their room, the group comes across a Double Battle being held in one of the Club's rooms between a Trainer's Watchog and Mienshao and another Trainer's Heatmor and Emboar. Ash finds out more about Heatmor on his Pokédex. Mienshao uses Drain Punch on Heatmor and Watchog lifts and Slams Emboar onto the ground. The other Trainer declares that he will show everyone the true power of the "Fire Warriors" and orders Emboar to use Hammer Arm on both opponents and for Heatmor to do the same with Flame Burst. Flame Burst creates a fiery explosion and knocks out both of the opponent's Pokémon, winning the battle for the Fire Trainer, whose name is Shamus.
After the battle, Ash, Iris, and Cilan are walking down a hallway when they see Shamus talking to the Trainer he beat earlier, whose name is Kylan. Shamus demands to see the Trainer's Pokémon so that he can take one as winnings from the battle. Iris runs over to tell him that this is wrong and Cilan says that he should not be doing this, but Shamus brushes them both off. Don George appears and thanks the two Trainers for the great battle, defusing the situation. Shamus leaves and the group asks Kylan why he would have a Pokémon battle with such high stakes, but he says that he didn't even want to battle in the first place and that Shamus wanted to get his hands on powerful Pokémon. Ash and Cilan agree that this is not what Pokémon battles are for.
In the cafeteria, Cilan announces that lunch is ready while all the Pokémon eat their food. Tepig notices Shamus sitting at another table by himself and begins to remember that he used to be his Trainer, and so runs toward him excitedly. Ash sees Tepig running off and apologizes to Shamus for his disturbance. Ash asks Tepig to come back, but he doesn't leave Shamus's side. Cilan wonders if the two know each other. Iris reminds Ash that Tepig was abandoned by his original Trainer, making Ash remember finding him tied up and malnourished in Accumula Town. Cilan is shocked at this revelation since he was not traveling with Ash at the time. Ash asks Shamus if he was the one who abandoned Tepig, and he replies saying Tepig was lucky Ash gave him a break. Iris and Ash scold him and say that it was wrong to throw a Pokémon away. Ash demands that he apologize to Tepig, but Shamus refuses and throws him to Ash. Cilan gets in the middle and says that the only way to settle this is with a trial, and it just so happens that he's a judge connoisseur. The cafeteria suddenly turns into a spacious courtroom with Cilan as judge, Tepig as plaintiff with Ash as his counselor, Shamus as the defendant, and Iris, Pikachu, Snivy, Emolga and Axew as the audience. Shamus's defense is that he left Tepig for his own good because forcing a weak Pokémon into battle would be worse than abandonment. Iris, Snivy and Emolga all yell at Shamus saying that he's really rude, but Cilan makes them be quiet, which they aren't happy about. Ash prosecutes by mentioning the rope that tied Tepig to a post. Shamus argues that he had to tie Tepig up to keep him from following. Cilan is unable to decide a verdict, so Don George interrupts and suggests a battle to settle the argument. Shamus agrees only if it is a Double Battle. Ash tells Shamus that he would have to apologize to Tepig if he loses. Snivy approaches Ash and emphatically volunteers to battle with Tepig. Cilan reminds Ash that Snivy had trouble with her Trainer as well. Ash agrees to Snivy's wishes and the two Trainers decide to battle in the morning.
Later that night, Tepig goes outside on his own to think. He has a flashback of when Shamus abandoned him and begins to tear up as he remembers being tied up. Ash's voice calls out for Tepig, and so he shakes away the tears. The rest of the group, including Snivy, come around a corner and say that they have been looking for Tepig. Ash tells Tepig that he and Snivy want to train, but sighs and lowers his head. Cilan says that Tepig may not want to battle his former Trainer, prompting Iris to tell Tepig, "There's such a thing as being too nice." Snivy goes up to Tepig and slaps him with Vine Whip and begins to talk passionately. Tepig then agrees to battle.
The next morning, the battle between Shamus and Ash is about to begin. Though Snivy is ready, Tepig still appears downtrodden. Ash commands Snivy to use Leaf Storm on Emboar, but it dodges. Ash tells Tepig to use Flamethrower on Heatmor, but Tepig can neither bring himself to battle nor dodge a Hammer Arm from Emboar. Ash tells Tepig that he understands how he feels. Shamus chuckles and says that he pretends to be sad and on the verge of tears whenever he abandons a Pokémon to make it think that he actually cares, all so that it follow him. Upon hearing this Tepig becomes immobilized by sadness and mentally breaks down. Snivy tries to help Tepig, but it is no use. Realizing this, Ash asks Snivy to cover for Tepig. Snivy uses Attract on Emboar, leaving him helpless to avoid Vine Whip. Shamus snaps Emboar out of it by having Heatmor use Fury Swipes on its teammate. Emboar recovers from the infatuation and uses Flamethrower while Heatmor uses Fire Spin. Snivy dodges, but the two attacks hit Tepig. Then Snivy is struck by Heatmor's Fury Swipes and Emboar's Heat Crash. Snivy eventually manages to get back up and tries to get Tepig to battle along with Ash. Finally, Tepig decides to battle. Tepig uses Flame Charge, hitting both Heatmor and Emboar, but Shamus is not impressed. Both Emboar and Heatmor get back up and use Flare Blitz Fire Spin, respectively. Emboar launches forward, enveloped in blue flame, and is boosted by the Fire Spin spiraling around him. Impressed by the technique, Cilan calls this the "Super Flare Blitz." Tepig is about to be hit by the powered-up attack, but Snivy pushes him out of the way and takes the blow, knocking her out. Ash thanks her and says that she deserves a good rest, but she wants to stay and watch her teammate battle. Seeing everyone encouraging him, including Snivy, Tepig teems with the determination and begins to glow. Because of his friends love and support, Tepig evolves into Pignite. Despite this, Shamus says that Pignite still has no chance of winning. Ash commands Pignite to use his new move, Fire Pledge. Pignite strikes the ground, sending a pillar of fire that engulfs both Emboar and Heatmor. Ash tells Pignite to finish with Flame Charge, knocking Shamus's Pokémon out and winning the battle for Ash. Everyone congratulates Pignite as he and Ash hug, with Snivy in Ash's arms. Given his victory, Cilan reaches the verdict that Ash was right. After recalling his Pokémon, Shamus walks over to Pignite and apologizes for what he did. He asks Pignite to ditch Ash and come back to his team, which makes Pignite smile with excitement. Pignite stares at his former trainer for a moment before using Flamethrower on him, charring him and turning his hair into an afro. Ash tells Shamus that Pignite is "one of the gang" and isn't going anywhere. Shamus runs away saying "I'll remember this!" The episode ends with everyone gathering around Pignite, celebrating his victory, evolution, and overcoming of his past. The group now resumes their journey towards Icirrus City.
As Watchog lifts Emboar off the ground while performing Slam, its nose is cream-colored instead of black.
Cilan says that Ash may have a hard time winning because of the Fire Warriors' special combinations. However, Cilan should not have yet known about these combinations, since Emboar and Heatmor had not yet used any of them.
When Emboar dusts himself off, the pattern on his side is missing.