Here is a team I peaked #28 with. It's based on Zard + Scarf Blacephalon breaking for each other + lure sets on Heatran (Nature Power) and Tornadus-T (Z-Focus Blast).
Charizard-Mega-X @ Charizardite X
Ability: Tough Claws
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Flare Blitz
- Dragon Claw
- Dragon Dance
- Roost
First of, Zard + Bulu has no defensive answer. Zard abuses Grassy Terrain. Bulu abuses bulky waters. Zard also deals with Volc and Kartana very well. I chose Roost, allowing it to stall break more efficiently. It also helps it in general to not faint from recoil. Earthquake would be used for Heatran mostly but opponents often scout for it, allowing you to get a first hit on Lando for a later sweep. Jolly Nature is used over Adamant to abuse DD the most efficiently, allowing you to outspeed Lele or Kyurem-B for example.
Tapu Bulu @ Leftovers
Ability: Grassy Surge
EVs: 248 HP / 164 SpD / 96 Spe
Careful Nature
- Horn Leech
- Superpower
- Swords Dance
- Protect
Bulu is the Zygarde and Ash-Gren counter. It also sets up the terrain for a Nature Power Energy Ball from Heatran. Protect is used over Synthesis to wear down Rain and Trick Room turns, also giving you a better match up against Tornadus-T. These invests allow you to better check Gren while outspeeding Azu and Crawdaunt. (You could run only 200 Spe since Crawdaunt doesn't do much anyway, or 222 if you want a better match up against Tyranitar.)
Heatran @ Leftovers
Ability: Flash Fire
EVs: 152 HP / 104 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Lava Plume
- Earth Power
- Nature Power
- Stealth Rock
Heatran is the Rock setter. It's also the Magearna check (with Blacephalon, eventually) + helps against Lele. These invests allow Heatran to at least speed tie with the other Heatrans, KOing them with Earthpower. The SpAtk also helps KOing Mega-Mawile.
104 SpA Heatran Earth Power vs. 252 HP / 0 SpD Heatran: 340-400 (88 - 103.6%) -- guaranteed OHKO after Stealth Rock and Leftovers recovery
104 SpA Heatran Lava Plume vs. 40 HP / 0 SpD Mawile-Mega: 246-290 (98 - 115.5%) -- 87.5% chance to OHKO
104 SpA Heatran Lava Plume vs. 40 HP / 0 SpD Mawile-Mega: 246-290 (98 - 115.5%) -- 87.5% chance to OHKO
Nature Power allows Heatran to KO bulky waters (except for Fini) for Zard or Blacephalon, becoming Energy Ball for Gastrodon, Thunderbolt for Mantine for example.
Tornadus-Therian @ Fightinium Z
Ability: Regenerator
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Hurricane
- Focus Blast
- U-turn
- Defog
Tornadus-T provides you with Defog support. It's also designed to lure in Heatran or Tyranitar and KOing them with Z-Focus Blast, helping Blacephalon cleaning. U-turn is used over Knock Off for momentum purposes, as the team is more of a Bulky Offensive build.
Tapu Koko @ Shuca Berry
Ability: Electric Surge
EVs: 104 HP / 12 Def / 176 SpA / 216 Spe
Timid Nature
IVs: 0 Atk
- Thunderbolt
- Hidden Power [Ice]
- Volt Switch
- Roost
Tapu Koko is the Pinsir and Hawlucha counter. Roost helps it pivoting on Toxapex and Zapdos more reliably. The HP and Def EVs + Shuca Berry allows it to survive one +1 Thousand Arrows from Zygarde after Rocks + to weaken Lando for Zard. Koko also provides momentum with Volt Switch, helping Zard or Blacephalon in against bulky Grass types.
Blacephalon @ Choice Scarf
Ability: Beast Boost
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Fire Blast
- Shadow Ball
- Flamethrower
- Trick
Finally, Blacephalon helps against Alakazam match ups. It also cleans pretty easily once Tyranitar/Heatran is removed by All Out Pummeling, Gastrodon by Nature Power Energy Ball and Toxapex weakened by Zard.
About match ups in general, this team does well against most of the meta, especially most Stall teams and the common Zygarde Mag HOs. However, it struggles against Rain with Swampert + Kingra unless you catch Pert with NP Energy Ball or Pelipper with NP Thunderbolt, as well as against Zard X against which momentum is crucial.
(Since I'm stupid I only downloaded replays and didn't upload them... But I recommend you to check out PokeaimMD's road to rank 1 episode where he plays it from ~1860 to ~1940 I'd say)