Costa first appeared as a Tirtouga in Growing Pains as a wild Pokémon in Nimbasa City. Noticing that White was struggling to capture a Pokémon, Black decided to catch Tirtouga to teach her what to do. Black then sent out Tula to weaken him and promptly caught him in a Poké Ball. After the capture Marshal reveals that he had previously owned Tirtouga but released him due to his extremely stubborn nature.
In Mine Mayhem, Black attempted to bond with Tirtouga with some training, but Tirtouga ignored his Trainer and swam away. When Black attempted to get him to listen an assistant of Clay's came over and told him that Clay was ready to have a Gym battle so Black hurries to the gym, Tirtouga in his arms. Upon arriving Clay attacked Black and Tirtouga with his Krokorok's Sand Tomb, whose attack irritates Tirtouga enough to counter-attack with Brine. Clay then sent out Palpitoad and had it attack with a powerful water attack and Hyper Voice, causing Tirtouga to cringe and retreat inside of his shell. Due to this, Clay sent out Excadrill to drill against the shell with Drill Run, but the attack ended up dealing no damage at all. Although he did well, Black decided to save Costa for later and recalled him.
He was later used as his final Pokémon to fight against Krokorok. Due to the lights in the Gym shutting off, Krokorok gained an immediate advantage due to being able to see in the dark and dealt heavy damage to Costa. When Krokorok was about to deal the final blow, Black imitated Costa's form, confusing Krokorok and causing it to miss. Using the opportunity, Costa attacked with Brine and knocked Krokorok out, earning Black the Quake Badge.
In The Battle Within, Black used Costa as his second Pokémon in his fight against Skyla, battling her Swanna. Black ordered Costa to use Ancient Power, but Costa simply looked at him annoyed. Frustrated Black yelled at Costa about how important the battle was to him and Costa responded by attacking Swanna and knocking it out. Despite initially listening, he refused to do anything against her Unfezant and allowed himself to be defeated.
In Decisions, Decisions, Black is taken to the Tubeline Bridge for training under Brycen. Brycen has Costa train with his three Vanillish. Black is then tasked to defeat the Black Empoleon biker gang, where Costa defeats the leader's Scraggy with a Hydro Pump.
In The Cold Hard Truth, Costa is sent out to battle Brycen's Vanillish and quickly defeats it with Scald. He next went up against his Beartic, who used its cold breath to freeze icicles onto its claws. Despite the increase in power, Beartic was unable to break Costa's defense and was sent flying away. Beartic then countered with Focus Blast and struck Costa in an unprotected spot, causing Costa to evolve into Carracosta. Due to his increased size, Costa was able to overwhelm Beartic with his strength and win the battle for Black.
In One Way or Another, Black and Costa faced off against Iris and her Druddigon in the semifinals of the Pokémon League. Costa begins attacking Druddigon, forcing Iris to make sure to prevent it from getting close. Druddigon then stomped the ground repeatedly as it used Bulldoze to deal super effective damage to Costa. However, thanks to Costa's Solid Rock Ability, the damage from the attack is halved, forcing Iris to send Haxorus out, as it has Mold Breaker as its Ability. Haxorus begins slashing at Costa with its tusks, which Costa barely managing to block. Costa continues to block Haxorus's attacks until he eventually clamps his jaw onto Haxorus's tusk. Using his tail to balance himself, Costa lifts Haxorus upwards and fires an Ice Beam directly at it. The attack successfully freezes Haxorus and defeats it, giving Black the win.
During Team Plasma's attack on the League in Triple Threat, Costa, Musha, Bo, and Tula were sent out to help Black's allies fight against the Team Plasma Grunts causing havoc below. Once they finished fighting the Grunts, Costa and the rest of Black's team returned to their Trainer shortly after he defeated N. The reunion was cut short when Ghetsis attacked Black in order to prevent the public from learning about N's defeat. With a team specifically designed to counter Black's, Ghetsis had the immediate advantage. With Musha's help, Black defeated Ghetsis by defeating his secret weapon, a Volcarona, and then unleashed a series of powerful attacks on Ghetsis's team.
In The Final Battle: Crushed Ambition, Costa worked alongside other Water-type Pokémon to try and put out the fire on N's Castle.