Hello Pokébeach. This is a deck I have constructed based on Xerneas and Xerneas BREAK. The strategy is quite simple: use Geomancy to quickly get Energy onto the board. Then, use Xerneas BREAK's Life Stream to hit for huge damage. Delphox works as a brilliant secondary attacker that can sometimes hit for even larger damage.
Pokémon: 17
4x Xerneas (STS)
3x Xerneas BREAK
3x Fennekin
1x Braixen
3x Delphox (FCO)
3x Tapu Lele-GX
Trainers:
4x N
3x Professor Sycamore
3x Guzma
2x Skyla
1x Brigette
1x Acerola
1x Brock's Grit
4x Ultra Ball
4x Max Elixir
3x Rare Candy
2x Enhanced Hammer
2x Field Blower
Energy:
13x Fairy Energy (Basic)
Pokémon: 17
4x Xerneas (STS)
3x Xerneas BREAK
3x Fennekin
1x Braixen
3x Delphox (FCO)
3x Tapu Lele-GX
Trainers:
4x N
3x Professor Sycamore
3x Guzma
2x Skyla
1x Brigette
1x Acerola
1x Brock's Grit
4x Ultra Ball
4x Max Elixir
3x Rare Candy
2x Enhanced Hammer
2x Field Blower
Energy:
13x Fairy Energy (Basic)