The Lost World of Gothitelle! (Japanese: スカイアローブリッジとゴチルゼル！Skyarrow Bridge and Gothiruselle!) is the 21st episode of Pokémon the Series: Black & White, and the 678th episode of the Pokémon anime. It first aired in Japan on March 3, 2011 and in the United States on June 25, 2011.
The last leg of Ash and the gang’s journey to Castelia City means crossing the massive Skyarrow Bridge. As our heroes attempt to cross it, they are stopped by an angry Gothitelle—who uses its psychic power to send them back to the past, when the bridge was still under construction!
A little girl named Sally offers them a ride to the city on the Water Taxi, and when our heroes board, they discover the same Gothitelle working on the boat with Sally. The two make a great team, helping the customers and handing out snacks, and Gothitelle seems very happy. Something terrible must have happened to make it so angry in the present!
Slowly, the pieces come together: when the Skyarrow Bridge was finished, the Water Taxi went out of business, Sally and her family moved away, and Gothitelle went off on its own. Now it’s trapped our heroes inside its memories and won’t let them free. Ash challenges the stubborn Pokémon to a battle, but they are interrupted by a woman who calls out to Gothitelle.
It turns out the woman is Sally, now grown up and trapped with our heroes inside Gothitelle’s memories! Sally talks to her old friend, letting Gothitelle know how much she misses their time together on the Water Taxi, and as the two of them reconnect, Gothitelle releases our heroes back into their own world.
After bidding goodbye to Gothitelle and thanking Sally for coming to the rescue, Ash and friends cross the bridge, finally making their way into Castelia City!
Ash and his friends near Skyarrow Bridge, which will lead them to Castelia City. As they step closer, they spot a Poké Mart, so Ash decides he will call Professor Juniper. Ash, not looking where he is going, almost bumps into a passing woman. He apologizes and allows the woman to go ahead of him into the Poké Mart. Iris walks up and tells Ash that he's still a little kid. Ash goes inside and contacts Professor Juniper via the PC. Ash tells Juniper that he caught a Sewaddle, which makes her proud. She asks Ash if he wants to swap Sewaddle with Pidove and Ash says yes. Soon enough, Ash has his Pidove again. Then, Ash spots the woman he almost ran into earlier staring at some photographs. Cilan realizes the photos have some age to them, and the woman merely calls them "Water Taxis" with no details and walks off, confusing the group.
The group steps outside, just as an eerie fog rolls in. Just then, an Officer Jenny rides by on her motorcycle. Cilan asks if she could clear the fog. Officer Jenny sends out her Swanna, which Ash scans with his Pokédex, and uses Defog, but to no avail. Suddenly, a car drives by, and Jenny chases after it as no vehicles should be driven in the fog. Ash, despite the risks, decides to cross the Skyarrow Bridge anyway. Iris and Cilan have no choice but to follow him.
Once they get on the bridge, Iris tells her Axew to stay in her hair. Suddenly, a a Psybeam is fired in front of the group as a warning shot, with a Gothitelle making it clear that it doesn’t want anyone to cross. Determined to get to Castelia, Ash calls on Snivy and she uses Leaf Blade, but Gothitelle blocks with Protect. It then uses another Psybeam attack, but Snivy counters with Leaf Storm. Suddenly, the ground below the group collapses.
Ash and the others wake up to find that they are back where they started, and see that the Skyarrow Bridge is now just being built. Just then, a young girl named Sally invites them to ride across the river in the "Water Taxi". Cilan figures that it will offer some insight, so they receive their ticket to board. Sally then introduces them to her Pokémon, a Gothitelle, which makes the group suspicious. As the crossing begins, another passenger asks the Captain if he's heard that the "Water Taxi" is going to close soon, and he says yes. This makes Sally and Gothitelle really sad. Cilan points out that the under-construction bridge diffidently looks like the Skyarrow Bridge, but he cannot rationalize how they would have time traveled. Suddenly, they reach land after a seemingly short journey but quickly realize they are back to where they started. Cilan suggests they must be a time loop, and thinks Gothitelle might be the key. Ash and Iris agree. So they walk over to Sally and Gothitelle, who are stocking up on more snacks for their next and final voyage. Ash asks Sally if Gothitelle is her Pokémon, and Sally says no, rather she has befriended it. Then the Captain, also Sally's father, calls his daughter over to ask her something. Then, the same fog rolls in from earlier and Gothitelle starts walking away, so the group follows it.
They follow Gothitelle to the same spot on the Skyarrow Bridge. Gothitelle looks hostile and blasts a Psybeam attack. Cilan finally has the answer: this is the same Gothitelle that's accidentally thrown itself, along with Ash, Iris and Cilan into a little dream world. Ash demands that Gothitelle return them, but it refuses. Cilan suggests that Ash battle it, so Ash sends out Snivy again. Gothitelle is angered and uses Psybeam once more, which Snivy dodges easily, though it breaks many parts of the bridge. Ash calls for Leaf Blade followed by a Vine Whip, but Gothitelle uses Double Team, confusing Snivy, as well as letting her get hit by a Psybeam. Ash orders another Leaf Blade, though Gothitelle uses Psybeam again, hitting Snivy once more. Snivy looks badly hurt. Ash asks Snivy if she can go on, which Snivy nods determinedly. Ash tells his Snivy to use Leaf Storm, which Gothitelle avoids by using Protect. Then, suddenly, Gothitelle uses Psychic as it prepares to throw the levitated parts at Snivy. Suddenly, the woman from earlier turns up.
The woman reveals that she is an older version of Sally and that the younger one was merely an illusion created by Gothitelle. Sally approaches Gothitelle, assuring it that they are old friends. She recalls the night the Skyarrow Bridge opened, which also ended the Water Taxi services. Gothetelle was drawn to tears at the time, but Sally invited it to join her and her father as they moved away. Gothitelle was saddened when Sally later went to train to be a doctor, and it escaped from their new home. After the recounts, they wipe each other's tears from their faces. Gothitelle faces the fact that it can't go back into the past, no matter how many memories it can recount. Gothitelle decides to send Sally, Ash, Iris, and Cilan back to the present. Sally suddenly notices Gothitelle on top of the bridge, which they say a tender goodbye. Sally asks if she can visit Gothitelle again, which Gothitelle nods before vanishing in a mysterious mist. Officer Jenny soon arrives and says how strange it was for the fog to go away so quickly. The group look at each other and laugh.
The group say goodbye to Sally, wishing all the best with her new job, and continue on their journey. They cross the Skyarrow Bridge and look at the Castelia City skyline, and Ash says he is ready to get his third UnovaBadge.