Mega Charizard Y is a Pokemon with amazing offenses and a good speed stat for blitzing through teams. Serperior is a generally shunned grass type in VGC due to being outclassed by Amoonguss, Lucicolo, and others. Greninja is very strong but very frail, and if it doesn't KO its usually game over. These facts only make the following sets even more shockingly unpredictable...
Mega Charizard Y @ Charizardite Y
Ability: Blaze
EVs: 252 HP / 100 Def / 4 SpA / 100 SpD / 52 Spe
Bold / Calm / Timid Nature
- Heat Wave
- Will-O-Wisp
- Tailwind
- Roost / Focus Blast
Heat Wave is still powerful spread even with the main focus being bulk, getting a sun and STAB boost. Will-O-Wisp cripples physical attackers like Landorus-Therian, Tailwind is always useful for speed control, letting offensive allies safely run an Adamant or Modest nature. Roost for healing, Focus Blast for Incineroar and Tyranitar
Serperior @ Sitrus Berry / Light Clay
Ability: Overgrow / Contrary
EVs: 40 HP / 20 Def / 36 SpA / 200 SpD / 212 Spe
Timid Nature
- Taunt / Reflect
- Grass Pledge
- Light Screen
- Glare
Guess what? MORE SPEED CONTROL LOL. Taunt to stop Protect, Reflect to make physical moves even weaker, you'll see why Grass Pledge is here in a moment, Light Screen to halve special damage (Discharge is prevalent after all), Glare to paralyze.
Greninja @ Life Orb
Ability: Protean
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
- Water Pledge
- Dark Pulse / Surf
- Blizzard / Ice Beam
- Protect
Greninja is a sweeper. Water Pledge + Grass Pledge slows the enemy down even more, leaving them severely crippled, and with Serperior's screens and Charizard's Will-O-Wisp, Greninja isn't useless if it doesn't KO anymore. Dark Pulse to slam Trick Room Pokemon, Surf is spread, Blizzard is also spread but is rather inaccurate so you can go with Ice Beam, which is 100% accurate but weaker and only hits one opponent. Protect to scout and block moves for a turn.
The Mega Charizard Y set is inspired by popular Talonflame sets in gen 6 VGC. Charizard is bulkier, so I use it instead.