Tag Team Battle Inspiration! (Japanese: タッグバトルは友情バトル！イーブイ初参戦！！A Tag Battle is a Friendship Battle! Eievui's First Time in a Fight!!) is the 90th episode of the XY series, and the 889th episode of the Pokémon anime. It first aired in Japan on October 1, 2015, in Canada on November 21, 2015, and in the United States on November 28, 2015.
In Anistar City, where Serena is rehearsing for the next Pokémon Showcase, our heroes get a nice surprise when their friends Tierno and Shauna arrive with newly evolved Pokémon! Serena’s new friend Eevee is skittish and shy in the presence of so many others, and she suggests a Tag Battle so Eevee can gain some experience and confidence.
The matchup features Ash and Tierno versus Serena and Shauna! When Tierno and his Blastoise go into their usual battle dance, Eevee starts toe-tapping right along with them, and soon it’s leaping and whirling faster than Blastoise can follow! It gets one good hit in with Swift as Serena watches, starry-eyed...and then she asks everyone to put the battle on hold so her team can rehearse a new performance idea!
Ash and Tierno happily continue the battle on their own as Serena and Shauna go off to practice—because the next morning, it’s time to register for the Showcase!
After Chespin makes a sudden appearance and tries to chase an intimidated Eevee, Tierno arrives with his Blastoise and greets everyone. As Bonnie plays with Blastoise, Ash and his friends are surprised when Shauna and her Ivysaur turn up as well. Shauna, who has also come to participate in the Anistar Showcase, is greeted enthusiastically by Serena. Although Eevee is frightened by the presence of strangers, Serena gently reassures her new Pokémon and introduces her to Shauna. After Shauna expounds on Serena's wide range of performance opportunities for Eevee, everyone heads inside for some food and Tierno explains that although Trevor was supposed to meet up with everyone as well, he found a new Pokémon that he had yet to take a photograph of. Tierno then reveals, much to everyone's surprise, that he already challenged the Anistar Gym but failed to earn a Badge there.
Meanwhile, Bunnelby is still staying close to Eevee in order to help her feel more comfortable with her new friends. After witnessing Bunnelby give Eevee a Poké Puff, Chespin nervously approaches with a Poké Puff of its own and offers it to Eevee, but she is still afraid of Chespin and refuses to take it. While she comforts Eevee, Serena tells Shauna and Tierno about Eevee's gift for dancing, but Shauna points out that in a well-attended event like a Showcase, Eevee is liable to get extremely nervous on stage. To help Eevee adjust to traveling with Serena, several of Ash's and Clemont's Pokémon stand in a line to be introduced to Eevee one by one. Eevee successfully makes a small connection each with Dedenne, Frogadier, and Pikachu, but Chespin is unable to maintain composure as Eevee approaches it and accidentally frightens her away again. Later, Serena reassures Eevee and learns that Eevee very much wants to perform with her new Trainer, but has trouble building up the confidence to do so.
After Aria, the Kalos Queen, appears on television, Serena recalls the time she met Aria and the advice she had been given. Her memory of that day inspires her to challenge Shauna, Tierno, and Ash to a tag battle in order to help build Eevee's confidence. Everyone gathers outside at the battlefield again, preparing for battle - Ash's Pikachu and Tierno's Blastoise against Shauna's Ivysaur and Serena's Eevee. Pikachu and Ivysaur use Electro Ball and Energy Ball, respectively, and the moves cancel each other out in midair. Blastoise then enters the fray with a Rapid Spin attack, which is deflected by Eevee's quick use of Protect. After Blastoise dodges a Razor Leaf from Ivysaur, Pikachu uses Thunderbolt and aims at Eevee. Eevee, who is frightened by Pikachu's attack, trips over her feet and is unable to dodge the powerful move, but is saved by Ivysaur's timely intervention. Serena, Bonnie, and the Pokémon watching the battle all cheer Eevee on, and Eevee begins to feel more reassured as she gets ready to continue the battle. Tierno and Blastoise start their rhythmic dancing, and Eevee easily dodges Blastoise's carefully timed Water Gun and begins dancing herself, effectively confusing Blastoise. At this, Pikachu and Ivysaur jump back into the battle with moves of their own as Eevee lands a powerful Swift attack on Blastoise.
Suddenly, however, Serena asks to stop the battle. Watching Eevee battle Blastoise has given her a new idea for a performance, and she wants to start training right away. She and her Pokémon head to another area to rehearse, and Shauna decides to do the same while Ash and Tierno begin a one-on-one battle against each other instead. Meanwhile, Serena asks Eevee to teach her, Braixen, and Pancham how to dance for the upcoming Showcase, and Eevee agrees. The next morning, everyone is running late and races to the Pokémon Showcase so Serena and Shauna can sign up before registration closes.