I think the one word that best describes Kommo-O is versatility. (Also being oddly similar to Mega Altaria, at least in terms of stat distribution. Seriously, they're almost exact but with Kommo-o being a little bulkier and faster. Mega Alt has the Pixilate ability though, and a better typing so...) It can run both physical and special sets, and mixed sets as well and any sort of item from Specs, Scarf, Band, Leftovers, WP (maybe), AV, and beyond. Some are more viable than others, obviously, but it does create a lot of unpredictability. With its coverage, it has what it needs, but could certainly do better, especially on the physical side. I personally don't know about CC (Which obvs is powerful but lowers both defenses which is kind of Kommo-o's thing) unless it's a Choice set where switching out is encouraged, but Drain Punch would be a godsend on this thing, so that it starts making the most of its bulk, which is where I think it will find the most use that isn't done better by other things. However, Sky Uppercut isn't that bad. It's a 5 less BP Play Rough, and plenty of pokemon use that. Some kind of priority would be neat as well, and the ability to boost the special attack through Calm Min/Q But enough of talking about what it doesn't have, but rather, what it does provide you with. You have a great offensive typing, balanced stats, a usable movepool, some solid abilities, and a... decent defensive typing. Not great, but not awful.
When using Kommo-O, I operate under the idea that fairy types are a no-go. You can always run poison jab, sure, but I say it's better to save Kommo-O till the fairy's are gone, if possible. And let's be real. You have 5 other team members that can be used to deal with fairies, and your other weaknesses too. But if we look past the fairy weakness, we have a typing with 7 resistances and 4 weaknesses. We do have things that handle us pretty easily, but our typing also gives us the ability to set up on a good amount of things as well, plus we resist Stealth Rock, and we have useful defensive abilities that while somewhat situational, can be invaluable in the right situation. So, uh, it's no Mega Altaria as far as typing goes, but our defenses aren't ultimately wasted... as long as we account for fairies.
(Unrelated, but I do kind of wish GF had gone all the way and gave it like Recover to really help stand out among dragons, but oh well.)
With all that out of the way, I wanted to share some ideas for sets that try to make out of the bulk we have. SubBulkUp is a good place to start.
Kommo-o @ Leftovers
Ability: Soundproof / Bulletproof
EVs: 248 HP / 252 Atk / 8 Spe
Adamant Nature
- Substitute
- Bulk Up
- Sky Uppercut
- Outrage/Dragon Claw
I think a good start to looking at Kommo-O like this is to see it as a SubBulkUp Fighting-type that happens to get STAB Dragon rather than as a dragon that can get fighting stab. As such, this sets goes full HP, full Atk, with an adamant nature to make us as bulky and hard-hitting as possible. The goal isn't to outspeed things here, but rather slowly get boosts and start hitting hard, and while our 85 speed, especially uninvested isn't very good, it will still outspeed a lot of defensive/tank mons which is what this set is mainly for dealing with. This is where Drain Punch or Mach Punch would be the best use if we had it. We could be like a better, faster Conkeldurr with this. But alas. Dragon/Fighting is good neutral coverage, and like I said before, just avoid fairies at all cost, or make sure you have answers to fairies with the rest of your teams, and you should be golden. Outrage is my preferred move just to make sure we are hitting as hard as possible going off our somewhat lacking 110 Atk, but Dragon Claw is an option if you want to be able to not get locked into a dragon type move. The ability depends on you. Soundproof can negate certain moves altogether, like pixilate hyper voice, but Bulletproof can give you certain switch in opportunities. Overcoat is interesting as well, but feels a bit more niche.
Another variation would be to be run something like this.
Kommo-o @ Chesto Berry
Ability: Soundproof / Bulletproof
EVs: 248 HP / 252 Atk / 8 Spe
Adamant Nature
- Rest
- Bulk Up
- Sky Uppercut
- Outrage/Dragon Claw
With this set, you can boost, take a hit or two or absorb status, then rest it up and start back at full health. It's only a one time solution, but its utility is not be underestimated. Otherwise, it will act basically the same to the above Bulk Up set.
Dragon Dance is interesting because there are definitely other pokemon that can abuse this set well while being faster and harder hitting. It wouldn't necessarily be my first option for a Kommo-O but since we do have a certain niche in not minding SR and given our bulk, I feel like a bulky dragon dance set is the best DD set for us.
Kommo-o @ Leftovers/Life Orb
Ability: Soundproof / Bulletproof
EVs: 252 HP / 252 Atk / 4 Spe
Jolly Nature/Adamant Nature
- Dragon Dance
- Rock Slide/Shadow Claw/Poison Jab/Earthquake
- Sky Uppercut
- Outrage/Dragon Claw
The goal with this set is to get multiple DD's first and foremost. With the Given ev's and even a jolly nature, you only outspeed up to unboosted Garchomp, basically, which is neat but not great. So obviously you want at least two. With two DD boosts and a jolly nature, you outspeed essentially the entire unboosted metagame plus up to +1 base 88. Which is neat. If you're going adamant, then it's a bit less impressive only hitting 414 after two DD's, but the boost in power is needed, and kind of needed, so it's up to you. And as always, if you want to invest in your speed more so to outspeed certain benchmarks, then go right around. Leftovers gives you your only form of recovery, but life orb will obviously make you hit that much harder. Given our attack, it is worth considering.
But anyway, this is fairly standard as a Bulky Dragon Dancer. We'll want at least two to really start hurting things, and from there, we are pretty set. Your coverage move is dependent on what you want to deal with. Rock Slide provides you with the most supereffective hits and since Aegislash is banned, nothing else resists. Shadow Claw is good for the neutral coverage, while Poison Jab is for fairys but again, I'd rather not deal with them, and a +2 or +3 neutral hit will do just as well. Earthquake is an option, though the coverage is redundant, a 100 BP move is always nice. Grass/Fairys will wall you out totally, though, so it's not the best choice.
Finally, while there are other options to be sure, I wanted to throw out a SubSalac berry set for Kommo-O based off one I use for my Garchomp which has served me well before.
Kommo-o @ Salac Berry
Ability: Soundproof / Bulletproof
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Substitute
- Swords Dance
- Sky Uppercut
- Outrage/Dragon Claw
Is sort of the best of both worlds of a dragon dance and swords dance set, and works well once executed. The goal is to sub yourself, get a swords dance in and either sub until you hit 25% or just take a hit and get in the range naturally to activate your salac berry and sweep from there with +2 Attack/+1 Speed. Obviously, the set is troubled by priority, but once it gets going, it has the abiltiy to hit hard and do damage. Given that Kommo-O doesn't have the same attack or speed as Garchomp, it isn't AS effective, but definitely worth considering. You will end up just barely outspeeding base Pheremosa which is a pretty good benchmark to hit. From there you just use that STAB and hope for the best. (Again, avoid fairies like the plague or save till late-game)
I do want to try and tinker with a more utility-based set that makes the best of some of its defensive capabilities, and interesting moves later on, but that's just some different ideas for sweeper/wallbreaker sets. And that's not even counting the special sets! Kommo-o has tons of versatility and unpredictability that will aid in its journey. It will have a lot of competition from the other OU dragons, but I think if it focuses on what it can do best; be bulky, then it has great potential. At worst, it'll be a UU staple. If Hydreigon can thrive in UU with its 4 times fairy weakness, then so can Kommo-o