Dueling Heroes (Japanese: うずまきカップ！みずのコロシアムでだいバトル！！Whirlpool Cup! A Big Battle in the Water Colosseum!!), is the 216th episode of the Pokémon anime. It was first broadcast in Japan on September 20, 2001 and in the United States on October 26, 2002.
As the final round of the Whirl Cup begins, Ash and Misty must each face formidable opponents. Ash has his Kingler transferred from Oak's lab in preparation, but when he and his Totodile begin their first battle, they must face an opponent with a powerful Kingdra. Misty also faces a challenging duel with an experienced opponent and his Qwilfish. Meanwhile, Team Rocket sets about stealing an ancient jewel used in a reward ceremony to be performed for the tournament's victor.
A large crowd has gathered in the stands and the participating Trainers are in gondolas as the Whirl Cup tournament's opening ceremony begins. The announcer explains the history of the event and brings everyone's attention to the Sea Priestess, Maya. She congratulates them as well as wishing them a little luck. Maya shines her Great Sea Spirit Sapphire towards the sun, and Team Rocket who are working as food vendors, spots their next target to steal. Maya evokes the Sea Spirit Union, and a blue light washes over the entire stadium complex to bring forth the energy of all Water Pokémon. The announcer declares that prize given to the crowned Alpha Omega will be is a Mystic Water pendant.
The sixth round pits Ash against Christopher. Ash uses Totodile for this round and his opponent calls out a Kingdra. Ash scans Kingdra with his Pokédex and is pleased to see a tough opponent. Though Brock in the bleachers comments that Ash might not have a good time with this one because it's a dual Water and Dragon-type, making Totodile's Water attacks practically useless. Ash takes the lead and commands Totodile to dive under the water, but Kingdra counters with a Twister. Christopher orders Kingdra to stop the Twister causing Totodile to freefall. Kingdra aims a Water Gun, but Totodile lands on one of the platforms. Christopher decides a Hydro Pump is order, but Totodile simply walks along the attack and gets close enough to do a Headbutt. Kingdra dives to evade and Totodile does the same. Kingdra releases a Smokescreen to cloud the water. With no other option, Ash tells Totodile to jump out of the water. The battle comes to a standstill as Ash anticipates Kingdra's next move. Totodile begins to dance around, and this sign reassures Ash that everything will be fine. Fed up, Christopher has Kingdra resurface and try another Hydro Pump. Though Totodile Bites onto Kingdra's snout, effectively stopping the Hydro Pump. Kingdra swells to enormous proportions as a result. After a while Totodile releases its jaw and Kingdra goes flying across the stadium. It hit the water field hard and floats to the surface, knocked out. Ash wins the match and can advance to the next round. After the match, Team Rocket is still devising a plan to get Maya's staff, but they are interrupted when another staff member tells them that there are more hungry customers to serve.
Overnight, Misty stares at the Colosseum from her Pokémon Center room window. Ash offers her some reassurance, and Misty declares that she is simply excited for upcoming match. Day two of the Whirl Cup begins, and Misty goes up against Harrison in the ninth round. Harrison is one of the older Trainers, so he has a snobbish attitude when he steps up to the arena. The match is on, Corsola against Qwilfish. Qwilfish begins the match by shooting a Water Gun, but Corsola reflects it back with a Mirror Coat. Seeing that this tactic won't work, Harrison orders Quilfish to start swallowing water. As the announcer says that this is used for preparing a volley of spikes, Misty thinks fast. Qwilfish soon releases a Pin Missile and so Corsola counters with Spike Cannon. The two attacks explode in mid-air knocking Corsola back, but Qwilfish took refuge in the waters. Taking advantage of this, Qwilfish strikes Corsola with a Take Down attack. Worried that Corsola is going to burn out anytime, Misty tells it to use Recover, however Qwilfish has already started up another Take Down. By the time Corsola has recovered, Qwilfish's attack hits. Corsola and Qwilfish dip into the water, but the pair resurface and Quilfish is revealed to be stuck in Corsola’s crown of horns. Misty finally gets an idea and tells Corsola to use Spike Cannon. Corsola fires a close range Spike Cannon which sends Qwilfish sky-high, and Misty wins the match. During the battle, Team Rocket make their move towards Maya's staff, but Officer Jenny orders them to leave the restricted area, which foils their attempt.
Back at the Pokémon Center, Ash and Misty both congratulate each other on making it to the second round. A large commotion alerts the group to the screen featuring the match ups for tomorrow's second round battles. It turns out that Ash is up against Misty for the next round, and the two friends stare at each other in shock.