Familiarity Breeds Strategy! (Japanese: ライバル決戦！サトシ対シンジ！！Rival Decisive Battle! Satoshi VS Shinji!!) is the 186th episode of the Diamond & Pearl series, and the 652nd episode of the Pokémon anime. It first aired in Japan on August 5, 2010 and in the United States on December 18, 2010.
The first quarterfinal battle of the Sinnoh League at Lily Of The Valley Island has Ash pitted against his rival Paul. This round is a full battle, with each side using a full party of six Pokémon. As Ash switches out his first three Pokémon—Pikachu, Infernape, and Staraptor—there’s something quite familiar about it to Paul. In fact, Ash appears to be using the same Pokémon team he used in their first full battle at Lake Acuity! Paul begins the battle with Aggron, then Gastrodon, and brings his Drapion out after the first two are quickly defeated.
Watching the battle on television, Paul’s brother Reggie notices that Paul is well aware of Ash’s strategies. Reggie is convinced that Paul allowed Ash to take the first two wins as part of his overall plan!
After Ash switches Staraptor out for Buizel, Drapion catches Buizel in its pincer tail! We leave the scene with Ash screaming at Buizel to “get out of there!”—and as the action gets more and more intense, we have no choice but to wonder how this incredible match will ultimately play out!
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Having both progressed through the initial rounds of the Lily of the Valley Conference, it's finally time for Ash and Paul's long awaited league battle. With Brock, Dawn, Barry and Piplup (acting as a cheerleader) watching from the stands, Team Rocket selling snacks to the audience and ChampionCynthia and Charles Goodshow observing too, both competitors are brought into the main stadium where they will conduct a Full Battle to decide who will get through to the semi-finals. Ash decides to begin with Pikachu, and Paul sends out his first Pokémon, Aggron. The two Trainers face off, both aiming to settle their long-standing rivalry once and for all...
The action then shows a flashback of Ash preparing for his battle against Paul by getting in some last-minute training alongside Gliscor, which has recently returned from its training with McCann the Air Master. Gliscor practices Giga Impact in a session with Dawn's Mamoswine while Barry watches from Ash's side. After commending his Pokémon on how much its improved since being left for training, Ash reflects on his pastbattle with Paul, on how badly he lost and how much he's hoped to have improved. Ash reflects on how he has been thinking since Lake Acuity about how Paul's Pokémon became as strong as they did, saying that Paul takes everything he's learned in battle, and uses it to his advantage. Barry remarks that Ash does the same thing, but Ash says that because he'd been thinking about how Paul got to where he is now, he needed to look at everything he's been through while on his journey. Barry asks if Ash figured it out, but Ash replies that Barry will just have to wait until the battle, much to Barry's frustration, remarking that if Ash is going to keep him waiting, he'll "fine him big time!"
Inside the Pokémon Center, Dawn preps Piplup and gives him his new cheering uniform. Meanwhile, Paul talks to Reggie about his upcoming battle with Ash just as Dawn enters the lobby looking for her friends, but she quickly ducks out of sight. Reggie regrets not being able to be there, but Paul understands that he cannot just drop his Breeder responsibilities. Reggie asks Paul if he wants to reconsider which Pokémon he'll be taking into the match, but Paul confirms he's satisfied with his line-up. Reggie notes how glad he is that Paul met Ash, as he knows that no other trainer has influenced his brother as much. Reggie then advises Paul to not underestimate Ash, but to power through the battle and win. Paul thanks Reggie and ends the call, then discovers Dawn eavesdropping and as they walk outside, Paul confesses his main problem with Ash... his talk about bringing out a Pokémon's inner strength and how any Pokémon has the potential to be strong reminds him a lot of Reggie. Dawn points out to Paul that just as Reggie is Reggie, Ash is Ash and does things his own way. Everyone soon meets outside, and Paul tells Ash that he will see him on the battlefield to which Ash agrees.
Returning to the present, Paul begins by having Aggron use Metal Claw, and Ash has Pikachu counter with Iron Tail and the two Steel-type moves impact canceling each other out. Paul then tells Aggron to use Metal Sound. A high-pitched noise is produced from Aggron's horns which causes pain to Pikachu. In the stands, Meowth is also affected and can barely move, leading Jessie and James to cheer for Ash in order to make sure no-one notices Meowth. Piplup is also affected by the attack as Brock explains that Metal Sound lowers a Pokémon's Special Defense. Ash instructs Pikachu to use Thunderbolt to stop Aggron's attack, and Pikachu manages to pull it off, stopping Aggron as well as causing a little damage. Pikachu then uses Volt Tackle, speeding towards Aggron. Paul counters with Aggron's Flash Cannon, hitting Pikachu and sending him flying, rolling back onto his feet. Ash knows Pikachu is struggling and decides to call him back to save for later and substitutes with Infernape. Cynthia recognizes Infernape as the Chimchar she once battled while Team Rocket are excited to see Infernape battle, having had a soft spot for it since the Tag Battle Tournament. Paul tells Aggron to use Double-Edge while Ash tells Infernape to counter with Flare Blitz. The two powerful and dangerous attacks collide. The two are sent backwards, and Infernape suffers from the recoil. Unfortunately, Aggron has the Rock Head Ability which cancels out the normal recoil from Double-Edge... but luckily for Ash, it turns out that Aggron has suffered burns from Flare Blitz. Ash then instructs Infernape to use Mach Punch, and Paul orders Aggron to use Flash Cannon, but Infernape lands the fast Mach Punch before Aggron can fire, sending Aggron flying into the wall behind Paul and crushing the surface on impact. When the smoke clears it is unable to battle, giving Ash the lead.
Paul then sends out his Gastrodon and Ash calls back Infernape and sends out Staraptor. Gastrodon begins with Muddy Water and Staraptor uses Quick Attack and connects; Gastrodon continues using Muddy Water, circling its head above its body, and clips Staraptor. It quickly becomes clear that Gastrodon is using Ash's Counter Shield technique. Ash instructs Staraptor to dive down and use Aerial Ace, and Gastrodon counterattacks with Body Slam, trapping Staraptor with its soft body. Gastrodon then uses Water Pulse and shoots it straight up into the sky, which then picks up speed as it comes down. Gastrodon watches it intently; Ash and the gang realize that it will jump away at the last second, giving no time for Staraptor to dodge it. Just when all seems lost, Ash has Staraptor use Close Combat by banging hard into the ground, lifting him up, which knocks off Gastrodon and he escapes the Water Pulse. Paul orders Gastrodon to use Ice Beam while falling backwards, bringing the in-flight Staraptor to a screeching halt and crashing onto the field. Knowing Staraptor is at a big disadvantage since Gastrodon knows Ice Beam, Ash decides that he will have to recall Staraptor for later and change his strategy.
Ash calls back Staraptor and sends out Buizel. At this point, Paul points out that what Ash is doing is too predictable now. He knows Ash is just trying to get rid of all the frustration his Pokémon felt from that loss back at Lake Acuity into his advantage here which is why he brought them all back for this battle. Ash states he is correct and that this is all what his Pokémon want. He knows they lost to him back at Lake Acuity, but they are still beating him here no matter what. Buizel agrees immediately to what Ash has said. Gastrodon uses Ice Beam again and Buizel uses Aqua Jet, turning it into Ice Aqua Jet to hit Gastrodon. This hits Gastrodon and causes it to jump up and Gastrodon then goes for Body Slam, and Ash thinks quickly and instructs Buizel to meet the attack with Ice Punch, causing Gastrodon to faint.
Ash settles himself, adjusting his cap and knows that the hard part of the battle has only just begun. At home in Veilstone City, Reggie watches the broadcast, remarking that Paul had a back-up plan of Gastrodon using Ice Beam if Staraptor escaped, and wonders if Ash figured out that Paul had planned to sacrifice Aggron and Gastrodon all along in the first place. If not, he will need to do so right away.
Paul sends out Drapion and attacks with Pin Missile, which Buizel cancels out with its Counter Shield technique. Drapion then uses Cross Poison, which Buizel dodges by sliding behind Drapion. Buizel uses SonicBoom at Drapion's back, who blocks the attack with its tail. Drapion grabs Buizel with its tail, twisting around its torso to menace the struggling Buizel and ending this segment of the battle.