DanielJames' VGC Team (done by Marcusube)

Blaziken-Mega @ Blazikenite
Ability: Speed Boost
Level: 50
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Protect
- Flare Blitz
- Low Kick
- Rock Slide

Greninja @ Life Orb
Ability: Protean
Level: 50
EVs: 4 Atk / 252 SpA / 252 Spe
Naive Nature
- Gunk Shot
- Low Kick
- Ice Beam
- Protect

Thundurus @ Yache Berry
Ability: Prankster
Level: 50
EVs: 164 HP / 60 Def / 12 SpA / 20 SpD / 252 Spe
Timid Nature
- Nasty Plot
- Thunderbolt
- Psychic
- Taunt

252 Atk Terrakion Rock Slide vs. 164 HP / 60 Def Thundurus: 116-138 (66.2 - 78.8%) -- guaranteed 2HKO
252 Atk Tyranitar Rock Slide vs. 164 HP / 60 Def Thundurus: 120-144 (68.5 - 82.2%) -- guaranteed 2HKO
Takes Rock Slide AND residual damage from weather if weather is present

Ferrothorn @ Rocky Helmet
Ability: Iron Barbs
Level: 50
EVs: 204 HP / 96 Atk / 12 Def / 196 SpD
Relaxed Nature
IVs: 0 Spe
- Power Whip
- Gyro Ball
- Leech Seed
- Protect

252 Atk Terrakion Close Combat vs. 204 HP / 12+ Def Ferrothorn: 146-174 (83.4 - 99.4%) -- guaranteed 2HKO
252 Atk Parental Bond Mega Kangaskhan Low Kick (100 BP) vs. 204 HP / 12+ Def Ferrothorn: 122-146 (69.7 - 83.4%) -- guaranteed 2HKO
96 Atk Ferrothorn Gyro Ball (136 BP) vs. 252 HP / 124+ Def Mega Gardevoir: 174-206 (99.4 - 117.7%) -- 93.8% chance to OHKO

Aegislash @ Leftovers
Ability: Stance Change
Level: 50
EVs: 252 HP / 48 Def / 172 SpA / 36 Spe
Modest Nature
IVs: 0 Atk
- Substitute
- King's Shield
- Shadow Ball
- Flash Cannon

252 SpA Gengar Shadow Ball vs. 252 HP / 0 SpD Aegislash-Shield: 98-116 (58.6 - 69.4%) -- guaranteed 2HKO
252+ SpA Heatran Heat Wave vs. 252 HP / 0 SpD Aegislash-Shield: 96-114 (57.4 - 68.2%) -- guaranteed 2HKO
172+ SpA Aegislash-Blade Shadow Ball vs. 244 HP / 72+ SpD Thundurus: 81-96 (43.7 - 51.8%) -- 1.6% chance to 2HKO after Sitrus Berry recovery
This damage roll allows you to hit right under the amount it takes to pull the Sitrus Berry
172+ SpA Aegislash-Blade Shadow Ball vs. 4 HP / 0 SpD Mega Gardevoir: 122-146 (84.7 - 101.3%) -- 18.8% chance to OHKO
172+ SpA Aegislash-Blade Shadow Ball vs. 252 HP / 4 SpD Mega Gengar: 168-198 (100.5 - 118.5%) -- guaranteed OHKO

Gastrodon @ Rindo Berry
Ability: Storm Drain
Level: 50
EVs: 252 HP / 44 Def / 100 SpA / 108 SpD / 4 Spe
Modest Nature
- Scald
- Earth Power
- Ice Beam
- Recover/Protect

252 Atk Aerilate Mega Salamence Double-Edge vs. 252 HP / 44 Def Gastrodon: 184-217 (84.4 - 99.5%) -- guaranteed 2HKO
100+ SpA Gastrodon Ice Beam vs. 4 HP / 0 SpD Mega Salamence: 172-204 (100.5 - 119.2%) -- guaranteed OHKO
0 SpA Amoonguss Giga Drain vs. 252 HP / 108 SpD Gastrodon: 156-184 (71.5 - 84.4%) -- guaranteed 2HKO
252 Atk Parental Bond Mega Kangaskhan Double-Edge vs. 252 HP / 44 Def Gastrodon: 191-227 (87.6 - 104.1%) -- 12.9% chance to OHKO