Of course pokemon that can kill both Garchomp and Skarmory pretty easily (Charizard, Thundurus, Starmie) are very annoying but since this core is based around hazards stacking it is important that you can 1. set up your hazards and 2. keep your hazards on the field
Threats to this core were mainly pokemon that could defeat both and prevent them from getting up their hazards because they are forced out, but it will still leave the incoming pokemon unharmed. Another thing many people seem to forget is that stallbreakers, and Taunt users in general, also really annoy this core. Fairy types are of course great partners but they still leave you vulnerable to Mew, Talonflame and Gengar with Taunt, while Charizard X and Mega Altaria are still big threats.
Another important thing about this core is to keep the hazads you laid on the field. There are two ways to do this
1. Have a pokemon that threaten most defoggers. This is also great with the hazards, as you can threaten the pokemon 1v1 and the switchins are crippled by hazards. One example would be Kyurem-B, who can threaten defoggers such as Mandibuzz and Zapdos while also beating Thundurus, Manectric and Raikou. Pokemon that switch in against Kyurem-B, like Scizor and Ferrothorn, are crippled by spikes and stealth rock.
2. Taunt. Pretty obvious, a fast Taunt prevents Defog and also beats defensive cores. Bisharp and Serperior are also options to discourage the use of Defog, but they fail to beat many of the threats to this core so I will ignore them.
I decided to go for the second one (anyone who reads this can now steal Kyurem-B

) and my choice was Heatran.
Heatran @ Chople Berry
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Magma Storm / Fire Blast
- Earth Power
- Stone Edge / Flash Cannon
- Taunt
Heatran gives the core support on many different points. First of all, Taunt prevents pokemon such as Zapdos and Mew from using Defog, which helps keeping the hazards up. It is a nice switchin against non-eq Mega Altaria and non-eq Zard X, who are both big threats to the core and it beats electric types like Raikou, Thundurus and Mega Manectric. It also helps with a big threat to the core which is Taunt. Heatran beats Taunt Talonflame (if Stone Edge) Mew, Thundurus and Gengar (the latter two because of Chople Berry) which is a very big advantage over other pokemon. Stone Edge helps against Taunt Talonflame and Charizard Y (Chople Berry means you can live a Focus Blast) while Flash Cannon is a better option to beat Mega Altaria, Kyurem-B and Clefable.
Heatran does have its disadvantages. The core is still weak to water type wallbreakers, such as offensive Mega Slowbro, Starmie and Azumarill. Heatran also gives both Excadrill and Starmie the opportunity to rapid spin the hazards away as it is forced out by them. Don't want to make a whole team or anything but as a 4th teammate you can use pokemon such as Mega Scizor, Kyurem-B and Tangrowth who work really well with the core and also love seeing their checks being worn down by hazards.