The Mystery of the Missing Cubchoo! (Japanese: ソムリエ探偵デント！消えたクマシュンの謎！！ Connoisseur Detective Cilan! The Mystery of the Missing Cubchoo!!) is the 40th episode of Pokémon: BW Rival Destinies.
While training for the upcoming World Championship Junior Cup in Lacunosa Town, after the battle with Pignite and Mamoswine, Ash, Dawn and the others meet a young boy that Jervis knows who lives in the neighborhood in Undella Town named Chris. He apparently lost his Cubchoo just this morning when it disappeared from his family's Pokémon house to the outside. So Cilan, the Master Detective Connoisseur is on the case to solve "The Mystery of the Missing Cubchoo". Will he find the Cubchoo?
Ash and Dawn train, as Pignite tackles Mamoswine, who takes down Pignite. Mamoswine uses Hidden Power, which Pignite dodges and uses Flame Chage. Mamoswine is hit, so retaliates using Ice Shard, which is countered by Flamethrower. Mamoswine uses Take Down, followed with Hidden Power, which Pignite counters using Flame Charge. Cilan declares the battle as a tie and both trainers call their Pokémon back. Piplup would like to battle as well, but Cilan prefers to have a break. Jervis appears, claiming they are just in time. Jervis serves them tea and introduces Chris, a boy looking for Cubchoo. Chris tells them Cubchoo disappeared, so the heroes volunteer to find it for him, introducing in the process. Oshawott comes out, introducing himself with Piplup and both are amazed by Meloetta.
The heroes search around the area, but find nothing. Cilan asks Chris to tell them everything he knows about Cubchoo. Chris replies Cubchoo lived in a Pokémon house, a building specially designed for it. They enter the house and see it is a playground. Chris replies Cubchoo rarely went out, but even then it was for a walk. Chris shows them Cubchoo's bed; the last night they played a lot and Chris left Cubchoo in its bed and locked the door. Chris tells them the door is the only way in. Cilan smells a crime, announcing "detective time". Cilan asks for more info and Chris replies he opened the door at 7 PM and locked it in 9 PM. Iris tells Dawn Cilan does these things some of the time, even if he is a great chef. Dawn sees Cilan reminds her of Brock, for he flirted with every girl, giving her and Ash some trouble.
Cilan suspects someone came, unlocked the door, took Cubchoo, locked the door and jumped over the wall. Chris replies it is impossible, for the alarm system would go off if someone crossed the wall. Cilan thinks they must've dug a tunnel. He searches and finds footprints of a Pokémon, leading to a small tunnel. Piplup goes through, showing Cubchoo must've gone through it. Cilan analyzes the dirt, thinking Cubchoo must've gone through the tunnel several times. Ash passes through, so they think Cubchoo escaped to the forest. They go to the forest and Piplup bashes a Joltik, who uses Electroweb on him and Oshawott.
Oshaowtt and Piplup fight each other for this incident, so Meloetta calms both of them with her song. Ash informs Chris Meloetta sings this song to calm everyone down. Cilan finds more footprints and wonders if that Pokémon took Cubchoo. Axew finds some leftovers, so Cilan asks to find some berries. Iris jumps on a tree and spots some. Meanwhile, Team Rocket find a target and dive under the sea. The heroes follow the footprints and find a Beartic, who is eating the apples. Surprisingly, it does not attack them. Cilan thinks Beartic thought Cubchoo was from its pack and took it away from the house, though Iris and Dawn do not know how could it crawl through the tunnel. Cilan, Ash and Chris try to interrogate Beartic, who throws an apple away. Cilan sees they are given a silent treatment, so they look for Cubchoo themselves.
They find nothing, so return to Beartic. Cilan declares it is a prime suspect and notices Beartic's nose has Cubchoo's part of the nose. Cilan deduces Cubchoo went out, for Chris forgot to lock the door and crawled through the tunnel. It encountered a powerful Pokémon, so evolved into Beartic, but retained the nose. He pushes Chris to Beartic, but Chris finds that hard to believe. Dawn knows there is one way: Chris can call it back into its Poké Ball. Chri does that, but Beartic does not return, for it is not Chris'. However, the heroes notice a Cubchoo and a Larvitar playing around. Dawn asks Cilan how does he explain that, but Cilan sees it is all logical. Larvitar befriended Cubchoo and last night, it opened the door to let Cubchoo out, then locked the door, crawled through the tunnel and left to play with Cubchoo.
Dawn asks about Beartic, so Cilan replies it is an ordinary Beartic, who was just hungry. Cilan declares the mystery solved, but Iris scolds him, for he is a pain, depressing Cilan. The heroes ask Chris did he have a Pokémon Battle. Chris replies he hasn't, so Iris asks Ash to show Chris a true battle. Ash does that, challenging Larvitar by sending Scraggy, who immediately leers Cubchoo and Larvitar. Scraggy starts by headbutting Larvitar, who retaliates by biting him. Scraggy uses High Jump Kick, but Larvitar dodges, causing Scraggy to be hit. Larvitar uses Sandstorm, knocking Scraggy away, who uses Focus Blast. Larvitar uses Hidden Power, hitting Scraggy. Dawn declares the battle as a draw.
Cubchoo is inspired Lavitar, wanting to battle as well. Chris replies they need to tell everyone it is fine. Ash considers Larvitar to be Cubchoo's rival. Chris wants to participate in battles, so Ash replies he should go on a journey. Chris thinks he should train Cubchoo and catch Larvitar, so they can go to the journey. Later, Chris thanks them for finding Cubchoo. In the night, Team Rocket is diving via the submarine and found what they were looking for and go to report to Dr. Zager.
Who's that Pokémon?: Joltik (US).