Kommo-o seemed cursed when it first came out. A Dragon/Fighting type in the generation where fairies were cemented as the best type in the game, and below average speed for OU, good, but not fantastic abilities and stats, while all around good, were not exceptional. The USUM came out and gave Kommo-o an utterly busted Z-Move. Nuke your opponent and buff all of your generally good stats at once? ALL THE YES. Thankfully, even with the loss of Z-Moves Clangorous Soul proves that Clangorous Soulblaze is not forgotten. And Kommo-o's stats in conjunction with its amazing movepool belay its true strength, not that it is great at one role, but it excels at many and exploiting that fact is what makes Kommo-o a versatile threat that is to be respected.
Dragon Wall
Kommo-o
Item: Sitrus Berry/Leftovers/Assault Vest
Ability: Soundproof/Bulletproof/Overcoat
-Body Press
-Breaking Swipe
-Bulldoze
-Taunt/Protect/Dragon Tail
EVs: 252 HP/200 DEF/56 SPE
Nature: Impish (+DEF, -SATK)
A defensive doubles set. Body Press is the main STAB, and makes good use of Kommo-o's high Base 125 DEF. Breaking Swipe is secondary STAB and acts as an intimidate against the opposing team, while Bulldoze provides coverage and speed control. Last move is up to preference. Taunt is great at shutting down Trick Room, Protect (provided it is not being used), Rage Powder, Follow Me and other disruptive shenanigans, Protect is always a fantastic move for doubles and synergizes well with Leftovers, while Dragon Tail is an additional form of disruption, forcing out pokémon your foe may not have wanted out while doing damage at the same time and works with Assault Vest, making Kommo-o very resiliant on both sides of the spectrum.
Ability is up to personal preference. Soundproof is the most situational, considering Kommo-o resists every popular move aside from Boomburst and Clanging Scales which have poor distribution (though blocking Snarl is useful if running a special set). Bullet Proof blocks certain moves which are more common like Shadow Ball, Focus Blast, Aura Sphere and Sludge Bomb, giving Kommo-o situation immunity but allowing it to pivot effectively against certain targets. Overcoat is recommended for allowing Kommo-o to null powder moves (Rage Powder/Sleep Powder/Spore) and Hail/Sandstorm, both of which are pretty common in doubles.
EV spread and nature is for increasing Body Press's damage and maximizing bulk while giving a little speed, though can be tweaked to outrun faster opponents if need be.
Other Options
Stealth Rock -Best move in the game
Bulk Up/Dragon Dance/Swords Dance/Iron Defense -Kommo-o gets a lot of setup moves. Most pale in comparison to Clangorous Soul, but not having to sacrifice 1/3 of your HP is a significant draw
Substitute -Works especially well with Soundproof, meaning only Infiltrator Pokémon can bypass the sub.