Tag! We're It...! (Japanese: 全員参加！タッグバトル！！ All Members Participate! Tag Battle!!) is the 50th episode of Pokémon: Diamond & Pearl.
Ash and Brock think that Dawn should enter the Tag battle contest, even Zoey suggested she should enter. Dawn is a bit sckeptical, but with Piplup's persuasion, Dawn agrees to enter. Enta, the announcer, tells the Hearthome City Tag Battle Contest has been for bonding the hearts of Pokémon and people. It will take three days to complete. Each participant has a card with a number. On the screen will be two numbers - one for the participant and one for his/her tag partner. Dawn found his partner, number 9, named Conway. Conway tells Dawn Slowking has a liking for her. Brock is happy to know he has a girl for a partner, named Holly, who has a Wingull. Brock flirts with her and Croagunk prepares to stab him, but Holly declines him as a love interest. Ash is still looking for his partner, but the partner found him - it is Paul.
Paul is aggressive, even if Ash warns him to be polite. Pikachu goes to shake hands with Paul's Elekid, but gets shocked and pushed away. Pikachu is ready to attack Elekid and Ash tries to stop him, but gets electrocuted. Enta reveals the prize for winning the Tag battle is a pair of bells, the Soothe Bell. James thinks with the bell in his hand, he will attract each Pokémon. Enta tells the participants they have time to practice with each other before entering the Tag battles. Conway tells Dawn he studied their enemies' strategies and is sure to win. Holly goes with Brock to practice, while Ash is still mad about Paul.
First are Dawn and Conway vs. two trainers. Dawn sends Piplup and Conway his Slowking. The trainers send Scyther and Koffing. Conway advises to Dawn to attack, while letting Conway to be defensive. Scyther uses Razor WInd and Koffig Sludge Wave. Piplup uses Bubblebeam to stop Razor Wind, while Slowking uses Safeguard to protect from Sludge Wave. Koffig uses Thunderbolt, but gets negated via Slowking's Protect. Sycther uses X-Scissor, but gets stopped and defeated by Piplup's Peck. Koffig uses Gyro Ball, but gets stopped by Psychic and defeated by it. Dawn and Conway are the winners of the battle. Dawn is impressed and wants to know Conway's strategy, as it would improve her skills as a Coordinator.
Ash proposes Paul to do the similar, but almost gets burned by Flamethrower. Ash is excited for Chimchar to know the move, but Paul is not impressed, as it was weak. Ash goes to help it, but Paul stops him, as he does not want him to mess everything up. Dawn reminds them it is about the link between Pokémon and people. Citing Cynthia's words, Paul goes away with Chimchar. Ash asks him why he entered the competition in the first place and Paul responds to meet the Fire-type Pokémon. Brock recalls the first time Paul and Ash clashed Pikachu used Thunderbolt on Elekid, though this was to power Elekid up - now he plans to power Chimchar up.
Brock's Sudowoodo and Holly's Wingull face Yanma and Bagon. Wingull goes to use Blizzard, but gets stopped by Yanma's Steel Wing. Bagon uses Zen Headbutt, so Holly orders Wingull to control itself, but Brock knows there is no time, so Sudowoodo's Double Edge pushes Bagon away. The trainers begin to argue and Brock and Holly go to take advantage of it. Wingull uses Blizzard to hit them. Bagon goes to counter-attack with DragonBreath, though Sudowoodo uses Flail to attack it. Wingull uses Aerial Ace, hitting Yanma. With this, both Pokémon are defeated, ensuring Holly and Brock a victory. Brock goes to flirt with her, but stops, remembering her words. Still, Holly is impressed and thinks they could be the best Tag team the world would know.
Next are Ash and Paul vs. two trainers. Ash sends Pikachu and Paul his Chimchar, while the trainers Magmar and Rhydon. Ash warns Paul it will be tough, though Paul thinks Pikachu won't have much effect. Pikachu starts with Thunderbolt on Magmar, but it is redirected to Rhydon, who is not affected. Rhydon attacks Pikachu using Megahorn, damaging him. Paul tells Ash to stay out, but Ash reminds him they are both in this. Magmar uses Lava Plume, hitting everyone. Though Pikachu evades, Chimchar goes straight in. The attack strengthens up Chimchar, who retaliates with Flamethrower, hitting Rhydon. Rhydon attacks using Hammer Arm and goes after Chimchar, but gets attacked by Pikachu's Iron Tail. Magmar uses Protect, while Rhydon uses Surf, but Paul orders Chimchar to use Flame Wheel. Ash tells Chimchar to stop, but remembers Zoey's combination, so orders Pikachu to use Iron Tail.
With a spin, Pikachu's Iron Tail foils Rhydon's Surf and defeats it. Pikachu charges with Volt Tackle, while Chimchar digs. Magmar stops Pikachu with Fire Punch, but gets hit and defeated by Chimchar's digging. Paul and Ash win the battle. James and Meowth are impressed by Chimchar, but Jessie reminds them to focus on the bell. Though they won, Brock, Dawn, Conway and Holly think the separate efforts won, but will not get them the bells. Paul orders Ash to stay out of his way, but Ash reminds him Tag battles require teamwork, thing Paul has not shown yet.
This episode's name is a reference to the statement "Tag! You're it!"
When the first battle match ups are being shown, Paul's picture is shown instead of Conway's.