The Steel Flying type is good. Like really good. The number of times Pokémon run coverage just because they are otherwise shutdown by Steel Flying types is a testament to how good the type is and how good the Pokémon that possess it are. And thus Corviknight reigns supreme as the best early game bird. Fantastic typing above average HP and Defense and average Special Defense with reliable access to Roost ensures Corviknight sees consistent play.
Steely Feather Duster
Corviknight
Ability: Pressure/Mirror Armor
Item: Leftovers/Rocky Helmet/Heavy Duty Boots
-Defog
-Roost
-U-Turn
-Drill Peck/Body Press
EVs and Nature:
252 HP / 252 DEF / 4 SDEF
Sassy (+SDEF, -SPE)
Corviknight makes the most out of its support movepool. Defog is a game changing move, destroying your opponents spell and trap cards clearing away Screens and Entry Hazards, ensuring your team doesn't get savaged on switching in and removing what Protection your opponent sets up. Roost keeps Corviknight healthy throughout a game so it can Defog again and again. U-Turn along with a speed reducing nature allows Corviknight to act as a slow pivot, getting its teammate in safely for a hopefully favorable matchup. Drill Peck is for STAB and Body Press is good coverage. Leftovers and Heavy Duty Boots keeps Corviknight healthy, while Rocky Helmet causes chip damage on contact attackers.
Flock Tactics
Corviknight
Ability: Mirror Armor
Item: Leftovers/Rocky Helmet
-Tailwind
-Taunt
-Body Press
-Brave Bird/Protect
EVs and Nature:
252 HP / 4 DEF / 252 SPE
Jolly (+SPE, -SATK)
Corviknight makes for a durable Tailwind setter in the doubles format, able to take repeated abuse and setup Tailwind, while blocking Trick Room and Amoongus with Taunt. Mirror Armor serves as an effective block against Intimidate, punishing Incineroar, and Lando-T switch-ins. Body Press is so that Corviknight isn't completely passive. Brave Bird serves as coverage, while Protect is Protect. Rocky Helmet punishes Fake Out's directed to Corviknight, while Leftovers is for longevity.
Other Options
Pressure + Spite - Corviknight can go for a PP stall strategy. There are many moves with low PP in doubles, especially on restricted Pokémon like Zacian's Behemoth Blade, Calyrex's Glacial Lance/Astral Barrage, Kyogre's Water Spout, Stakataka's Gyro Ball, Palkia's Spacial Rend, Trick Room, Stone Edge, etc. Depriving you opponent of multiple uses of these moves is game changing. However, it is very situational. Most moves have 15+ uses (anything with 10 PP can be maxed to 16 PP) requiring multiple Spites. Even the 5 PP moves can be maxed to 8 PP which with Pressure and Spite would only drain 6 PP which is still enough for another use.