I have reached 1600+ elo in this format with this team, so I think this team needs a lot of improvements for reaching higher ladder!
Groudon-Primal @ Red Orb
Ability: Desolate Land
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Precipice Blades
- Fire Punch
- Rock Tomb
- Dragon Tail
Necrozma-Dusk-Mane @ Ultranecrozium Z
Ability: Prism Armor
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Dragon Dance
- Photon Geyser
- Sunsteel Strike
- Stone Edge
Xerneas @ Power Herb
Ability: Fairy Aura
EVs: 96 Def / 252 SpA / 160 Spe
Modest Nature
IVs: 0 Atk
- Geomancy
- Moonblast
- Hidden Power [Fire]
- Thunder
Rayquaza-Mega @ Life Orb
Ability: Delta Stream
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- V-create
- Dragon Ascent
- Extreme Speed
- Swords Dance
Marshadow @ Focus Sash
Ability: Technician
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Shadow Sneak
- Reversal
- Spectral Thief
- Counter
Yveltal @ Life Orb
Ability: Dark Aura
EVs: 4 Atk / 252 SpA / 252 Spe
Hasty Nature
- Dark Pulse
- Oblivion Wing
- Heat Wave
- Sucker Punch