SubPads Melmetal
Melmetal @ Protective Pads
Ability: Iron Fist
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Double Iron Bash
- Earthquake
- Substitute
- Thunder Punch / Thunder Wave / Ice Punch
Melmetal @ Protective Pads
Ability: Iron Fist
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Double Iron Bash
- Earthquake
- Substitute
- Thunder Punch / Thunder Wave / Ice Punch
Substitute + Pads Melmetal is a check to this core. It comes in on Kyurem with ease, sets up a substitute, and easily kills both Heatran and Kyurem with EQ and DIB. Melmetal even tanks a Magma Storm from full and OHKOs Heatran in return. While it obviously doesn't tank it as well as AV Melm, SubPads is a superior option because it doesn't run the risk of getting burned by Flame Body.
Not to mention, a Melmetal behind a sub is very hard to switch into even with team support. It easily 2HKOs any Lando because Intimidate doesn't go through sub. Pex never breaks its sub with any of its moves and can be defeated with quake + bash flinch. Even Helmet Slowbro isn't safe because it dies to TPunch + DIB flinch + a second TPunch, and Melm, and Melm obviously doesn't take the helmet chip. You can run TWave if you'd prefer to paralyze opposing Corviknight or Ice Punch if you want to hit Zapdos, as well.
Threats of the Round 
With Protective Pads shielding it from Flame Body and Double Iron Bash to bypass Kyurem's Substitute spam, Melmetal leverages its monstrous base 143 Attack and access to Earthquake to lay waste on this core. While I would have personally used a different spread to take Magma Storm more reliably and Substitute isn't truly necessary to defeat this core, Protective Pads Melmetal is undoubtedly a massive threat to it because it nullifies the fundamental strategy of luring and burning with Heatran on the switch when its using Double Iron Bash to threaten Kyurem. At last, its gargantuan physical bulk and Ice resistance allows Melmetal to neuter Kyurem pretty much all game long.
Thanks to amazing bulk and handy resistances to both Heatran's and Kyurem's STABs, Tapu Fini is a stone wall for the core to break through. Despite being more susceptible to Substitute + Pressure stalling than Melmetal, Tapu Fini does run Taunt to shut these shenanigans down immediately and Calm Mind to boost alongside either, which makes it a threatening win condition that can use both as setup fodder. While you can theoretically try to force some PP stalling and Flame Body activation around Draining Kiss, that's highly unreliable and mostly uneffective, making Taunt + Calm Mind Tapu Fini an exceptional threat to the core.
Additional Notes 
Choice Band Tyranitar isn't a durable check to the core by any means, but it still easily takes a couple hits from this core and Rock Blast makes it very threatening, especially because Stone Edge is the more common Rock STAB and the Kyurem user will be trying to scout what move Tyranitar locks itself into via Substitute. This scenario is quite favourable to the Kyurem user if Tyranitar is running Stone Edge, but it's extremely frightening when Kyurem is greeted by a suprise Rock Blast that can potentially KO it from 75%. Rock Blast also comes with the added perk of being a multi-hit move that doesn't make contact and hits Heatran for neutral damage, making it a fairly safe move to click against either.
Keldeo is obviously very threatening to this core, being a quick Ice and Fire resist with a secondary STAB that hits both and doesn't even make contact (or would care about burns in the first place), so it definitely deserves a spot here despite competing with its arguably better counterpart, Urshifu-Rapid Strike. However, in this particular task, Keldeo has a slight advantage over Urshifu and that is PP: Secret Sword has double the PP of Close Combat, making it noticeably harder to drain away through repeated Substitutes. That being said, Keldeo will more often than not be worse than Urshifu-Rapid Strike in almost everything else, meaning it's harder to justify over it, despite being better at fulfilling this particular niche.
Mixed Slowbro has a lot of potential against this core, being more adept at taking on Heatran thanks to a hefty Special Defense investment while still comfortably sitting in front of Kyurem and taking no damage from Icicle Spear. However, the set showcased fails to actually check Kyurem in the long run, as its Body Press by itself lacks any power whatsoever to threaten Kyurem and thus will get PP stalled without any issues. This matchup could be better if Slowbro used Future Sight over Scald, which would force more Roosts and Substitute out of Kyurem, which can be exploited via Teleport as well. Also, although unrelated to this particular task, running Body Press without Colbur Berry is suboptimal since you miss out on Slowbro's potential to lure and KO other big threats such as Weavile.
Round 16: Rotom-Wash + Tornadus-Therian 
Zygarde-10% is such an underrated Pokemon in my opinion because Thousand Arrows unexpectedly checks some meta Pokemon, such as 
Zapdos - but that's not what we're here for! Let's break this core!
Rotom-W with Thousand Arrows, meaning there's no status or Pain Split shenanigans to worry about. Just remember, 
Big Bird, you also win - utilizing either Thousand Arrows or Outrage - but you lose a lot in the long run because of Knock Off. Not much else to say.
The Sinnoh slug takes the crown here as the biggest threat to the core, with its auspicious typing and ability allowing it to totally blank Rotom-Wash and become the one to gain momentum, be it via easily switching into it or via forcing predictable double switches. On top of that, it has more than enough Special bulk to comfortably take on Tornadus-Therian and has access to Toxic in order to cripple both for the rest of the game.
While Choice Specs isn't the most viable or popular Tapu Koko set, it doesn't change the fact that it is a massive threat to the core. Not only is it a faster pivot that can force big damage on Rotom-Wash and outright KO Tornadus-Therian with ease, but it also comfortably switch into Tornadus-Therian and can take an Hydro Pump from Rotom-Wash without problems. Once again, relying on its item for power and lacking Roost make Choice Specs not the #1 best set to take on this core due to Knock Off and Hydro Pump, respectivley, but Tapu Koko is undeniably a big threat to the core no matter the set.
Everyone's favourite landshark performs pretty well against this core via the use of a Lum Berry, preventing it from being crippled by Rotom-Wash' Will-O-Wisp or Hurricane's confusion chance. Being able to grab a risk-free turn on either can put Garchomp in a position to not only destroy the core, but also leave sizable holes in the entire opposing team. However, the only issue is that Lum Berry itself isn't the most recommended item for Swords Dance Garchomp, which would appreciate Yache Berry, Roseli Berry or Leftovers a lot more often, especially given how unreliable Scale Shot's damage output is against Rotom-Wash.
Calm Mind Clefable comfortably sits on either member of the core and has an easy time setting up barring some para-fusion hax, which means it has no issues whatsoever switching in and blanking both Rotom-Wash and Tornadus-Therian. That being said, Clefable does nothing to stop the VoltTurn cycle they create, which means it will more often than not become just another victim of the cycle when the appropriate breaker or pivot comes in to force it out.
Weavile is one of the few Pokémon blessed with the ability to naturally outspeed and OHKO Tornadus-Therian, with is very useful in the context of this core because it also carries a strong, neutral Knock Off to hit Rotom-Wash for massive damage after a boost. However, Weavile faces big troubles while switching into either Pokémon and isn't reliable at disposing of Rotom-Wash in the first place, because it needs to find an opportunity for a Swords Dance and even then some Rotom-Wash have Defense investment rather than Special Defense and potentially carry no item just to thwart Weavile.
This would've been a threat but it got banned unfortunately
Round 17: Pelipper + Seismitoad 
