GamerOmega has some good sets listed with Zard and Cloyster. Another Zard Y set is
Charizard-Mega-Y @ Charizardite Y
Ability: Drought
EVs: 60 HP / 252 SpA / 196 Spe
Timid Nature
- Fire Blast
- Solar Beam / Roost
- Earthquake
- Flame Charge
The speed allows you to outspeed Landorus-T and outspeed scarf Lando after a Flame Charge. Earthquake is a 2HKO on Heatran which normally walls Zard Y and can get off an Ancient Power (which is rare) or Roar you back out onto Rocks which is another 50% you're taking for no reason. If you're playing on showdown or at level 100, try
Charizard-Mega-Y @ Charizardite Y
Ability: Drought
EVs: 72 HP / 252 SpA / 184 Spe
Timid Nature
- Fire Blast
- Solar Beam / Roost
- Earthquake
- Flame Charge
The sets essentially do the same thing, it's just more investment is needed at lv 50. If you go with GamerOmega's set, try only running 220 speed EVs isnstead of the EVs I listed above. It's enough to outspeed Kyurem-B which is the only other thing you're gonna want to outrun as Fire Blast is a guaranteed OHKO after Stealth Rock if he's running 0 HP / 0 SpDef
Run Foul Play Mandibuzz as well and not Knock Off. If you run Knock Off, you risk becoming setup fodder to any sweepers.
For Garchomp, try Impish nature instead of Adamant. Replace Outrage with Dragon Tail and then you can replace Stone Edge with Toxic so you can hit things like Rotom, Quagsire, etc it's for bulky water types mainly. I know how Toxic sounds; I wasn't too big on it myself first time I started running it but it's very useful and effective most of the time. That's the standard lead chomp / tank chomp set
Other than that, everything looks good. Hope this helps ^^