I have Diancie + Kommo-o, what threats should i watch out for with this core and what sweepers would be really good with this core
Hi
Take Azelfie, Diancie and Kommo-o seem to go pretty well together. I'm assuming you're running defensive SR Diancie and Specs Kommo, right? Some major threats you need to watch out for are Ground-types- Flygon especially because it can deal massive damage to both pokemon, and Nidoqueen also comes easily on Diancie. Shaymin is also a big threat because it comes in on Diancie and clicks Seed Flare, and it also carries Psychic so Kommo-o usually cannot even 1v1 it. Additionally, while Diancie is bulky on the special side, it doesn't really help Kommo-o all that much at taking Psychic and Fairy-types on, since pokemon such as Specs Espeon, Gardevoir, and CM Florges pressure it a lot. Finally Doublade and other steel types are quite a threat since they easily threaten Diancie and Kommo-o if it gets locked into Clanging Scales.
One example of a sweeper that might help you out is Nasty Plot Salazzle. Salazzle can severely pressure the fairy types that hurt your core, as well as steel types and even hard switch into Shaymin in a desperate situation. It usually runs NP, Fire Blast, Sludge Wave, and a Hidden Power with Poisinium Z or Firium Z. I would suggest running HP Ice here so as not to give Flygon a free setup opportunity. If you are running Salazzle, be sure to pack some solid ground resists/immunities, such as Mantine or a grass type.
Another sweeper that could be useful if you are trying to build a slower, more balanced team, is Snorlax. Snorlax easily switches into most of the Psychic and Fairy types that threaten the core, as well as Nidoqueen, and can set up on these pokemon. Diancie in return helps Snorlax by taking Knock Off, and providing Heal Bell support if you are running that. This makes your team weak to Doublade and Heracross, so make sure to pack answers to that such as Gligar. Kommo-o can also pressure Doublade heavily with Clanging Scales and in some cases even lure it for Snorlax.
Zoroark is another pokemon that could be run here. While it may make your team weaker against fairies, it can oustpeed a lot of the stuff that annoys your core such as Shaymin and Nidoqueen and threaten it with powerful Knock Offs. It can trap Specs Espeon and Gardevoir locked into Psychic with Pursuit, and Pursuit can also help it lure and trap Doublade and Reuniclus. Special Zoroark with Sludge Bomb can also be run, and this can give you a fantastic lure to some of the fairy types and help Kommo-o spam its dragon STAB.
Overall, you can really go any direction you want with these two pokemon. While they do share some synergy, they don't really share a whole lot of similar checks and counters, or cover a large portion of the offensive metgame. The RU metagame is a fun place for experimenting with a lot of different teambuilding styles, and lots of strategies are viable so don't feel constrained into any particular mons.
hope that helped!