The Semi-Final Frontier! (Japanese: シンオウリーグ準決勝！ダークライ登場！！Shin'ō League Semi-Finals! Enter Darkrai!!) is the 189th episode of the Diamond & Pearl series, and the 655th episode of the Pokémon anime. It first aired in Japan on August 26, 2010, and in the United States on January 22, 2011.
It's now time for the semi-finals of the Lily of the Valley Conference, and Ash has found himself up against Tobias, the Trainer who has managed to defeat all the SinnohGym Leaders and all the other competitors using only his Darkrai. As battle commences, Tobias unsurprisingly sends out Darkrai to battle first, whilst Ash sends out his Heracross. Brock comments that it's a good choice to use a Bug-type like Heracross against a Dark-type Pokémon like Darkrai. Tobias tells Darkrai to use Ice Beam whilst Ash has Heracross use Hyper Beam and the two attacks collide. Ash then commands Horn Attack, but Darkrai intercepts it with a Dark Void putting Heracross straight to sleep. Luckily Ash is prepared for this and calls out for a Sleep Talk, which turns into Megahorn. The Megahorn slams into Darkrai, who quickly rebounds and knocks out Heracross with a Dream Eater attack.
Ash recalls Heracross and sends out Torkoal, commanding a Flamethrower. Darkrai intercepts it with Dark Pulse and causes a huge explosion which sends Torkoal flying back and knocking it out. Now that two of his Pokémon have fainted, Ash knows Tobias and Darkrai are living up to their reputations. Ash decides to send out Gible next and has him begin with Rock Smash which manages to land a direct hit. Tobias calls for Ice Beam, and Ash orders Gible to keep dodging. Eventually Gible fires a Draco Meteor, but Darkrai dodges and uses Dark Pulse, knocking out Gible. Tobias compliments Ash on Gible's power, and admits that the Draco Meteor would have knocked out Darkrai had it made contact.
Ash sends out his next Pokémon: Sceptile, who has speed and power on its side. Darkrai fires an Ice Beam, but Sceptile dodges and uses Quick Attack, which Darkrai also avoids. Ash then orders Sceptile to use Leaf Storm but Darkrai dodges and hits with Sceptile with a close range Ice Beam. Sceptile is hurt and stumbles, allowing Darkrai to land a Dark Void and put Sceptile to sleep. Darkrai then attacks Sceptile with Dream Eater which hits Sceptile and causes him to react in pain from the attack. At this point, Sceptile is floating in his dream, wondering what's happening, when he hears Ash's voice calling to him and wakes up immediately in response much to Tobias's surprise and shock. Ash tells Sceptile to use Leaf Blade, and Sceptile strikes hard on Darkrai, finally managing to take the Pitch-Black Pokémon out of the fight. Everyone cheers for Ash, but Brock reminds Dawn and Barry that Tobias still has five other Pokémon to battle.
Tobias recalls Darkrai into its Poké Ball, impressed with Ash, admitting that he earned his spot in the semi-final rounds for accomplishing what no other Trainer could while battling him. For the first time in Sinnoh, he now has to send out a second Pokémon. Not worried in the slightest, he throws a Poké Ball into the air which releases Tobias's second Pokémon, a Latios.
The Eon Pokémon descends from the sky, strafes past an astounded Ash, Pikachu and Sceptile, streaks around the stadium, then heads over to Tobias, ready to battle. Ash can't believe what he's seeing, while an equally surprised Dawn looks Latios up on her Pokédex, which explains that Latios can fly faster than a jet plane. Barry is confident in Sceptile's abilities.
Ash tells Sceptile to use Leaf Blade on Latios, but Tobias is ready for this and commands a Giga Impact from Latios who is far faster than Sceptile. Latios hits Sceptile in mid-air, knocking it out in one hit, to Ash's shock.
Ash thanks Sceptile for a great job after recalling it, and sends out his Swellow to combat Latios next. The two let out a battle-cry at each other, and Brock and Dawn feel that Swellow has a very good chance of winning since it'll be able to take Latios on in the sky. Ash tells Swellow to use Quick Attack, and Swellow speeds forward. However, Latios easily dodges it. Despite its high speed, Swellow is no match for Latios and finds itself on the run from the Eon Pokémon. It manages to get behind Latios and tries another attack, but Latios once again dodges and begins chasing Swellow. Ash tells Swellow to head to the ground and then use Aerial Ace. Swellow flies up towards the sun blocking it from view and then descends quickly with Aerial Ace powered up. Tobias orders Latios to use Luster Purge, and Latios hits Swellow in the middle of the descent. Swellow crashes to the ground, knocked out with not a single blow scored on Latios.
Ash recalls Swellow thanking it for trying its best, but fights back tears as the reality of the situation sets in. He only has one Pokémon left to fight and he looks ready to forfeit. Dawn, Brock, and Barry, unwilling to see Ash give up, tell him that he could still make a comeback. Ash looks at the scoreboard, which displays the daunting fact that Ash has only one Pokémon left which Tobias still has Latios and four others. Pikachu is also upset at the seemingly hopeless situation but Ash tells Pikachu that he isn't giving up yet and Pikachu lets his Trainer know he's ready to battle. Ash pulls back his hat backwards and sends Pikachu in knowing that no matter what, he and his Pokémon will always give it their all. Despite having gained respect for his opponent, Tobias is certain that this will be their last bout, and hopes that they'll both do their best.
Pikachu starts off with a Quick Attack, and lands a small hit. Pikachu turns around and uses Volt Tackle and Latios spins around and uses Giga Impact to counter. The two attacks collide, and Pikachu comes out of it the worst as it is sent flying backwards. Wincing, Pikachu lands on its feet and watches as Latios flies into the air and begins another Giga Impact. Pikachu tries to intercept once again with Iron Tail, but like before is sent flying backwards. Latios flies high up in the sky until it was barely visible, then flies back down, a sparkling pink Luster Purge glowing at its mouth. Ash sees Pikachu lying on the ground injured, and orders Pikachu to dodge, which Pikachu does, the Luster Purge narrowly missing.
Latios flies by and arcs up back into the sky, and unbeknownst to it, Pikachu has managed to get onto its back. Latios turns and sees Pikachu hanging on tightly. Pikachu uses Thunderbolt on the flying Latios, causing severe damage. Tobias tells Latios to shake Pikachu off, and Latios flies around trying to shake Pikachu off. However, he is hanging on for dear life and uses Thunderbolt again, causing Latios more damage which is now beginning to take its toll. Tobias then orders Latios to use Light Screen, which cuts the power of Thunderbolt when Pikachu uses it again.
Pikachu tries again and again to knock out Latios but to no avail, while Latios flies high into the sky. Latios twists suddenly to descend and as Light Screen wears off, Pikachu loses his grip and starts falling. Latios lands inches from the ground and Tobias tells Latios to finish Pikachu with Luster Purge. Ash yells out for a Volt Tackle and Pikachu somersaults and dives directly towards Latios with Volt Tackle fully powered. The Luster Purge meets the Volt Tackle, but the Volt Tackle slowly cuts through. Pikachu's strength is waning and he is struggling to cut through the attack. Ash yells at the top of his lungs for an Iron Tail, which cuts through the Luster Purge fully and scores a direct hit on Latios, causing a giant explosion which nearly knocks Ash and Tobias off their feet and manages to knock out all of the monitors.
The battlefield is covered with smoke as everyone is desperate to see what happened. Eventually the smoke clears and it turns out that Pikachu successfully took down Latios but was also knocked out in the process. As Ash has no Pokémon able to continue, Tobias is declared the winner by default. Paul is watching the battle on TV and walks away, disappointed for Ash upon seeing him lose. Tobias approaches Ash and they thank each other for the battle. Dawn and Barry are upset over Ash's loss, but Brock points out that Ash was amazing and that this marks the first time he's ever made it into the Top 4.
Tobias is then shown defeating a Trainer's Magmortar with his Darkrai, winning him the Lily of the Valley Conference. Tobias is presented the Winners' Trophy by Cynthia and Mr. Goodshow as fireworks fire off around the stadium.
Later, Ash stands outside the stadium ready to get on his way when Dawn arrives and notes that although their journey together is ending soon, it feels like they've just begun. Brock then arrives and reminds them both that their journeys really are just beginning. Ash agrees, knowing he's still got a lot of work to do if he's ever going to get into the Champions League, while Dawn comments that she's got a lot to do if she's ever to become a Top Coordinator. Brock is happy to see that his friends still following their dreams, but this leaves him to wonder if he's following his own. Just then Barry turns up, telling Ash that while he might be stronger than him now, he plans to train and defeat him in their next battle. Ash laughs, and the two rivals say a final goodbye before Barry leaves, full of energy as always. And so, the gang prepare to set forth on the final leg of their journey back to Twinleaf Town.