Keldeo is an amazing Pokemon for Water teams, as its additional Fighting typing and high Speed allow it to pose a threat to opposing Steel-, Dark-, and Normal-types that would otherwise pose a threat to the team, such as Bisharp, Hydreigon, and Snorlax. As a stallbreaker, Keldeo punishes walls like Toxapex, Gastrodon, and defensive Seismitoad by stopping their dangerous passive moves like Toxic, Haze, Recover, and entry hazards with Taunt. With Calm Mind, it can set up to beat these walls while also letting Keldeo KO Pokemon like Ferrothorn and Corviknight. These boosts with Calm Mind also allow it to break Pokemon like Mandibuzz, Mew, and Aegislash with Hydro Pump. Scald can be used as an alternative to Hydro Pump due to its more reliable accuracy and chance to burn opposing Pokemon; however, the caveat to using this move is that it is significantly weaker than Hydro Pump without Calm Mind boosts. Keldeo's STAB move in Focus Blast allows it to break Steel-, Dark-, and Normal-types like Ferrothorn, Bisharp, Hydreigon, Indeedee, and Snorlax that Water teams would otherwise have a tough time getting through. Keldeo runs maximum EVs in both Speed and Special Attack so that it can maximize its offensive presence and outspeed key Pokemon like Hydreigon and Indeedee. This offensive presence is supported by Leftovers, which allows Keldeo to become more threatening when it sets up and also recovers health.

Keldeo forms a very strong offensive core with Pokemon like Primarina and Crawdaunt. Primarina appreciates Keldeo's ability to stallbreak and allows it to clean late-game with its Calm Mind set. Crawdaunt can also switch into Psychic-type attacks from the likes of Reuniclus and use its powerful Knock Off and Liquidation to break teams down. While Keldeo's ability to be an oppressive offensive threat is incredibly valuable, it still needs support from a lot of other Pokemon to achieve this goal. Defensive Pokemon in Seismitoad and Toxapex provide the team with an Electric immunity and a Grass neutrality, respectively. Seismitoad also provides Stealth Rock support while Toxapex offers support through Toxic, Toxic Spikes, spreading Scald burns, and wearing down opposing Pokemon to make it easier for Keldeo to break through them. Rotom-W is also a great partner, as it is able to switch into Flying-type attacks from the likes of Corviknight and Togekiss and can answer back with its own STAB Electric-type moves. It also provides Defog support to prevent Keldeo from being worn down by Sticky Web, Toxic Spikes, and other entry hazards. Pelipper can assist Keldeo by getting rid of key Grass-type Pokemon like Vileplume and Virizion with its STAB Hurricane, as well as support Keldeo with Drizzle, bolstering the power of Keldeo's Hydro Pump. Cloyster is another teammate that helps deal with Grass-types as well as Dragon- and Flying-types for Keldeo and appreciates its ability to keep Stealth Rock and other hazards off the field with Taunt. Lastly, Araquanid is a great support Pokemon, as it can not only threaten Psychic-types like Gardevoir, but also use Sticky Web to allow Keldeo to threaten more Pokemon, namely Heliolisk and Choice Scarf Indeedee.

While donning the Choice Specs, Keldeo becomes a very threatening wallbreaker that is very hard to switch into for types like Normal, Dark, and Ground. With STAB Hydro Pump, Keldeo is able to burst through walls like Mandibuzz and Corviknight thanks to its raw power. This along with its STAB Aura Sphere eviscerating most Normal- and Steel-types like Indeedee, Bewear, Ferrothorn, and Bisharp makes it extremely hard to switch into. Secret Sword is a good alternative to Aura Sphere if the little extra power and the ability to hit the Defense stat as opposed to the Special Defense stat is preferred, which is key in dealing with Pokemon like Snorlax. Keldeo also uses Icy Wind to hit some would-be threats on the switch such as Noivern, Vileplume, and Dragapult, and Scald to have a more reliable Water-type STAB move when needed. In order for it to maximize its offensive presence, Keldeo runs full EV investment in both Special Attack and Speed with a Timid nature. This boost in Speed allows it to outspeed key Pokemon like Mimikyu, Modest Alolan Raichu, and non-Choice Scarf Jirachi naturally.

Keldeo's offensive presence and ability to break open holes in the opposing team make it great as a partner for setup sweepers like Gyarados and Cloyster. Keldeo also helps get rid of prominent Grass-types like Appletun and Vileplume with Icy Wind. Crawdaunt and Primarina are offensive partners that can help out Keldeo by getting rid of annoying Psychic- and Dragon-types, respectively, while switching into their respective types. Crawdaunt in particular, while able to greatly improve the Steel matchup alongside Keldeo, also helps check Jellicent which completely walls Keldeo. Rotom-W is also a very invaluable teammate for Keldeo, as it can take Flying-type attacks from the likes of Corviknight and Togekiss and threaten them out with its own Electric-type STAB move and pivot using Volt Switch. It can also use a Substitute + Nasty Plot set that can break Pokemon like Jellicent and Toxapex, as well as provide support through Defog, which prevents Keldeo from getting worn down from hazards. Seismitoad allows Keldeo to have Stealth Rock support as well as providing it a switch-in to Electric-type attacks. Toxapex also helps take Grass-type attacks for Keldeo as a defensive pivot while using Toxic or Toxic Spikes to help wear down the opposing team. Pelipper sets rain, which gives Keldeo ludicrous amounts of power with its Hydro Pump and allows partners like Dracovish to help clean teams that were weakened by Keldeo's wallbreaking power. Araquanid is also very helpful in assisting Keldeo with Sticky Web to slow down faster threats like Heliolisk and Choice Scarf Indeedee.

Keldeo holds a niche over Urshifu-R on Fighting teams, as its much higher Speed lets it combat threats such as Choice Band Galarian Zapdos and Garchomp, and it also defeats physical walls like Skarmory and Galarian Weezing. Hydro Pump is Keldeo's strongest move, allowing it to easily break through bulky Pokemon such as Celesteela and Aegislash, which Fighting-type teams can often struggle against. Secret Sword defeats Pokemon that would otherwise switch into its Water-type attacks easily, such as Volcanion, Gastrodon, and Chansey. Scald is used alongside Hydro Pump to avoid risking a miss when Hydro Pump's power isn't needed, compensate for Hydro Pump's lacking PP, and burn foes that can switch into Keldeo such as Kommo-o and Dragonite. Flip Turn allows Keldeo to maintain momentum and take advantage of common switch-ins such as Toxapex, Slowking, and Galarian Slowking. Icy Wind can be used over Flip Turn to ease Keldeo's matchup against the aforementioned Dragon-types in Kommo-o and Dragonite, helping Fighting teams deal with them and shutting down their setup opportunities with Dragon Dance by reducing their Speed.

Cobalion provides a Fairy and Psychic neutrality and can deal with Pokemon such as Clefable and Hatterene, albeit in a limited fashion, as its bulk leaves much to be desired. It also provides utility with Stealth Rock and Thunder Wave. Toxicroak checks Water-types like Toxapex and Tapu Fini, and it can sweep Fairy-type teams, which Keldeo struggles against, with Swords Dance and Gunk Shot. Choice Band Galarian Zapdos is a threatening wallbreaker that muscles past Pokemon that Fighting struggles to combat, such as Slowbro, Celesteela, and Toxapex. Choice Scarf Terrakion provides a revenge killer, late-game cleaner, and way to defeat Flying-type Pokemon such as Thundurus-T and Zapdos. It also outspeeds and beats Electric-type Pokemon such as Tapu Koko. Choice Scarf Buzzwole provides a defensive backbone for Fighting teams, as it can switch into threatening Water- and Ground-type attacks from Pokemon such as Barraskewda, Excadrill, and Choice Scarf Landorus-T.