Dragapult's high base stats and varied move pool make it great even in doubles. High speed & access to Light Screen and Reflect also make it an ideal first Pokemon to set up defenses. Phantom Force also allows it to buy time during Dynamax.
Tyranitar's Sandstorm ability is helpful for Pokemon with Sand Rush. It is also able to deal damage using Stone Edge and has a high Sp. Def stat thanks to the Sandstorm bonus. Try to use this with the Weakness Policy.
Excadrill's high attack stat & good typing, coupled with Sand Rush, make it an excellent sweeper. It's a good candidate for Dynamaxing since it's able to boost its team's defense with Max Steelspike. Running Protect is also recommended on most builds.
Whimsicott's main role is as a Tailwind setter, boosting its team's speed. It's also currently popular alongside Arcanine, to activate its Justified ability with Bulk Up. It is strong Tailwind setter candidate overall.
Great attacker with two viable abilities. Intimidate is the most common and is useful for lowering opponent's attack. Justified is usable in certain combos too. Priority Extreme Speed is also excellent for finishing off opponents.
Togekiss is an excellent doubles Pokemon that is being seen more and more recently. With access to some great support moves like Follow Me and Helping Hand, as well as powerful STAB Flying and Fairy moves, it can fulfill both support and offensive roles at the same time.
Braviary is an alternative Tailwind setter that also has good offensive capabilities. It often works better with Excadrill than Corviknight, purely because they don't overlap in typing. Braviary's Brave Bird also hits significantly harder.
Gastrodon's Storm Drain ability redirects water moves to it and grants it Sp. Attack, making this Pokemon amazing in double battles. It's Ground type also gives it Electric immunity, easily switching into Rotom.
Fire typing is very useful against the many steel types currently in the meta. Access to Will-o-Wisp and immunity to Ground moves are also incredible. Volt Switch gives it freedom to swap out to other Pokemon after using Overheat.
Cinderace is useful due to its relatively high speed and strong moves. U-Turn allows it so swap out quickly, while Pyro Ball can make short work of some common Steel types in the meta, like Corviknight and Excadrill. Good candidate for Dynamaxing too, due to Max Knuckle.
Rhyperior's low speed makes it a good candidate for Trick Room builds. With an excellent 140 attack, a STAB Rock Slide that hits both opponents is extremely dangerous. Weakness Policy is currently the go-to item for Rhyperior.
Barraskewda is a surprisingly dangerous threat when given the opportunity to strike first. With Close Combat and Poison Jab, its move coverage is also quite formidable. This Pokemon works best on a Rain team.
Malamar's good typing and access to some excellent moves make it a good addition to many teams. Contrary also allows it to turn Intimidate into a boon, so make sure to switch it in vs. Arcanine or Gyarados.
Lucario's good typing and move coverage make a good addition to many teams. Capable of being both a physical and special attacker, Lucario is quite versatile. It also has the Justified ability, so it can be used alongside Whimsicott in a similar way.
Some particular moves are significantly more important in double battles than singles. Don't immediately assume you can bring over a Singles Pokemon into Doubles without changing its moveset.
Protect Is Far More Important
The move Protect will block all damage you receive for one turn (except from Max Moves). You'll find that Protect timing can determine the outcome of your matches, so it's worth running it on most Pokemon.
Multi-Target Moves Are Common
Bringing moves that can hit multiple targets is incredibly advantageous because you are effectively doubling a move's power. For example, Toxtricity's Overdrive and Discharge have the same 80 power, but Discharge will hit all targets (even allies). When using such moves, consider how your own Pokemon will handle it too. You can use this to your advantage to trigger a combo, such as Surfing your Coalossal to trigger Steam Engine.
Swap Positions With Ally Switch
Ally Switch is a move which allows you to switch places with an opponent. You can use this move to reposition an ally who is about to be hit with a dangerous move. It can catch your opponent off-guard, and a surprising amount of Pokemon can learn this, such as Dragapult, Rotom, Togekiss, and more.
Weather combinations are much more viable in double battles. Although it's possible to set up weather with Max Moves in singles, it's much more efficient to have another partner Pokemon to do it for you. This is one of the reasons why the Tyranitar + Excadrill combo is so popular right now. Consider creating a team that works around weather.