Maybe I will rate this, but I'm too lazy to write and explain everything.
Charizard-Mega-Y @ Charizardite Y
Ability: Blaze
EVs: 248 SpA / 8 SpA / 252 SpD
Modest Nature
IVs: 0 Atk
- HP Electric / Will-O-Wisp
- Substitute / Will-O-Wisp
- Blast Burn
- Solar Beam
Charizard is supposed to be a Special Suicide Attacker with Blast Burn. Not a Bulky Attacker. 1v1 is a fast and quick metagame where most Bulky Sweeper is not very good. And MegaZard Y is not bulky. Pokemon like Slowbro-Mega, Mimikyu, Alakazam-Mega need to be bulky (Mimikyu stalls with Curse, SlowBro sets up Iron Defense+Calm Mind/Amnesia, Alakazam-Mega use Encore+Disable Strategy).
HP Electric for hitting Gyarados (Most people won't mega evolve gyarados on the first turn because Solar Beam hits Mega Gyarados Super Effectively I think.), Greninja, Primarina, Slowbro-Mega and other stuff. Charizard doesn't need to use Roost. You can use Substitute against Swords dance Mimikyu, Dragon Dance Gyarados+MegaZard X, Z-Conversion PorygonZ, Blast Burn MegaZard Y, Reflect, Calm Mind users like Tapu Lele, SlowBro-Mega and other Setup Sweeper and Staller. Will-O-Wisp is SD Mega-Mawile and DD Gyarados-Mega's Christmas Gift.
Landorus-Therian @ Choice Scarf/Flyium Z
Ability: Intimidate
EVs: 252 Atk / 252 Spe / 4 SpA
Naughty Nature
- Earthquake
- HP Ice
- Superpower
- Fly
Again, Leafovers sucks in 1v1. Scarf is a better item. Also, almost no one use Bulky LandoT (Some people use Bulk Up LandoT). HP Ice can still 2HKO opponent LandoT. While Opponent LandoT
-1 252 Atk Landorus-Therian Fly vs. 0 HP / 0 Def Landorus-Therian: 117-138 (36.6 - 43.2%) -- guaranteed 3HKO
Superpower can 6HKO and Stone Edge can 4HKO. Because of Intimidate. Unless opponent LandoT has HP Ice, it can defeat opponent LandoT easily.
Fly and Earthquake are STAB. Superpower helps to defeat PorygonZ, Lopunny-Mega.
Magnezone @ Electrium Z
Ability: Sturdy
EVs: 252 SpA / 252 Spe / 4 HP
Modest Nature
IVs: 0 Atk
- HP Fire/HP Ice
- Flash Cannon
- Metal Sound
- Zap Cannon
Just for Gyarados-Mega? Then Magnezone is better. Its SpA (130) is better than Tapu Koko' SpA (95). Z-Zap Cannon hits Super Hard. Metal Sound Punishes set up sweeper. Sturdy guarantees at least one Zap Cannon/HP Ice/Flash Cannon at Gyarados, Charizard, Landorus and other stuff. Flash Cannon is STAB.