Tyranitar @ Assault Vest  
Ability: Sand Stream  
EVs: 252 HP / 184 Atk / 28 Def / 44 SpD  
Brave Nature  
- Stone Edge  
- Crunch  
- Flamethrower  
- Pursuit  

Takes Leaf Blade from 252 Atk Kartana and OHKOes in return with Flamethrower, used on an alternative version of the finals team with Mega Latias over Cresselia
Venusaur-Mega @ Venusaurite  
Ability: Chlorophyll  
EVs: 252 HP / 108 Def / 40 SpA / 64 SpD / 44 Spe  
Modest Nature  
IVs: 0 Atk  
- Sludge Bomb  
- Giga Drain  
- Hidden Power [Fire]  
- Synthesis  

This was the first centerpiece of a finals team, I noticed that Ezrael often couldn't break Mega Venu and the coverage could be really nice. In practice, it was forced to click Synthesis far too often and didn't have enough offensive output so anyone I was facing could usually just ignore it and double the other slot
Genesect @ Expert Belt  
Ability: Download  
EVs: 64 Atk / 216 SpA / 228 Spe  
Hasty Nature  
- U-turn  
- Iron Head  
- Ice Beam  
- Flamethrower  

Thanks to Expert Belt, OHKOes Yache Landorus-T with +1 Ice Beam, OHKOes Mega Metagross with Flamethrower, and generally does a lot more damage. Offensive Genesect paired pretty well with Mega Venusaur, just needed the rest of the team to handle Fire-types
Genesect @ Icium Z  
Ability: Download  
Shiny: Yes  
EVs: 64 Atk / 216 SpA / 228 Spe  
Hasty Nature  
- U-turn  
- Iron Head  
- Ice Beam  
- Extreme Speed  

A set Biosci suggested, at +1 it can OHKO Misty Seed Zapdos with Subzero Slammer. Using Icium also meant Genesect already had a way to OHKO Kartana, so we could fit Extreme Speed
w/ Ferro and AV Fini (Greninja-Ash) @ Waterium Z  
Ability: Battle Bond  
EVs: 252 SpA / 4 SpD / 252 Spe  
Timid Nature  
- Hydro Pump  
- Dark Pulse  
- Water Shuriken  
- Protect  

The centerpiece of the team I built for a potential faceoff against Bowman in finals, I had used Ash Gren back when Marsh was around and wanted to give it another shot, especially after seeing it work on the OU teams my teammates were building
Tapu Fini @ Assault Vest  
Ability: Misty Surge  
EVs: 252 HP / 72 Def / 64 SpA / 120 Spe  
Bold Nature  
- Moonblast  
- Icy Wind  
- Knock Off  
- Hidden Power [Fire]  

An amazing supporter for Ash Gren - slows things down with Icy Wind, takes 252 Atk Kartana Leaf Blade and OHKOes with HP Fire, Knocks off Berries and Eviolites, and generally pivots pretty well. Tapu Fini and Ash Greninja together took advantage of most switchins to Ferrothorn, so those three plus Mega Gengar and a Zapdos/Mega Manectric killer made for a pretty powerful team
Entei @ Rockium Z  
Ability: Inner Focus  
EVs: 216 HP / 156 Atk / 136 Spe  
Adamant Nature  
- Sacred Fire  
- Stone Edge  
- Roar  
- Protect  

I tried to put this on maybe six different builds I showed Biosci but it never ended up making the final cut. Rockium ensures Entei can OHKO Incineroar and Zapdos with a Continental Crush, and it still has Inner Focus Roar for Trick Room and setup. Fire typing and Sacred Fire to burn gives it a solid matchup against Genesect and Kartana and prevents things like Zygarde from setting up safely. Definitely could be a solid contributor to the right team
Suicune @ Waterium Z  
Ability: Inner Focus  
EVs: 252 HP / 92 SpA / 108 SpD / 56 Spe  
Calm Nature  
IVs: 0 Atk  
- Hydro Pump  
- Snarl  
- Tailwind  
- Roar  

Taken from GenOne, Hydro Vortex makes sure Incineroar is actually offensively threatened by Suicune
w/ LO Kingdra (Zapdos) @ Electrium Z  
Ability: Static  
EVs: 184 HP / 4 Def / 136 SpA / 184 Spe  
Modest Nature  
IVs: 0 Atk  
- Thunder  
- Heat Wave  
- Hidden Power [Ice]  
- Protect  

Decent contributor to HO rain, takes down Tapu Fini and Thunder + LO Ice Beam from Kingdra was usually enough for opposing Zapdos. The team had Pelipper for Tailwind already and the coverage Zapdos provides was really useful
Thundurus @ Life Orb  
Ability: Defiant  
EVs: 136 Atk / 120 SpA / 252 Spe  
Hasty Nature  
- Wild Charge  
- Superpower  
- Hidden Power [Ice]  
- Protect  

Also tried out Fightinium, but the gist is you have the ability to OHKO Incineroar, Landorus-T, and after a Defiant boost, Tapu Fini and Mega Gengar. Relies a bit too much on the rest of the team to take any hits but worked out okay in tests
w/ Rain (Moltres) @ Flyinium Z  
Ability: Flame Body  
EVs: 248 HP / 56 SpA / 80 SpD / 124 Spe  
Modest Nature  
IVs: 0 Atk  
- Hurricane  
- Burn Up  
- Tailwind  
- Protect  

Rain always wants Fire-type coverage for Ferro/Kart but never wants a Fire-type with an exacerbated weakness to Water. Enter Burn Up Moltres, which also has Supersonic Skystrike for Bulu and Amoonguss and Flame Body to punish U-turn spam from Genesect/Landorus-T
w/ Z-Ally Switch Lele (Chesnaught) @ Iapapa Berry  
Ability: Bulletproof  
EVs: 216 HP / 120 Atk / 172 Spe  
Adamant Nature  
- Zen Headbutt  
- Wood Hammer  
- Hammer Arm  
- Spiky Shield  

Probably the most out there thing I considered, Bulletproof makes you immune to Mega Gengar so with Tapu Lele on the field, you click Ally Switch, take nothing from the Sludge Bomb or Shadow Ball targetting Lele, and OHKO Gengar with Psychic Terrain-boosted Zen Headbutt. Wood Hammer's still decently strong, Chesnaught beats Amoonguss 1v1 unless it's running Clear Smog, and Hammer Arm keeps you from being useless against Incineroar. Doesn't do enough if those specific situations don't come up and it's useless with Gengar gone now but was an interesting idea