Kyogre

Kyogre @ Choice Scarf
Ability: Drizzle
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
- Water Spout
- Surf
- Ice Beam
- Thunder

This is supreme to primal. If someone tells you otherwise, they are WRONG. I can't recall how many times this thing has just swept teams simply because it's just too strong. The power behind a Water Spout is enough to take out nearly everything. Darkrai, Xerneas, nearly any pokemon in OU and under, Mewtwo (both mega forms), Yveltal, e.t.c.

I'll run a few calcs but honestly you don't need them.

252+ SpA Kyogre Water Spout (150 BP) vs. 104 HP / 0 SpD Xerneas in Rain: 456-537 (108.8 - 128.1%) -- guaranteed OHKO

252+ SpA Kyogre Water Spout (150 BP) vs. 0 HP / 0 SpD Mega Mewtwo Y in Rain: 382-451 (108.2 - 127.7%) -- guaranteed OHKO

252+ SpA Kyogre Water Spout (150 BP) vs. 4 HP / 0 SpD Darkrai in Rain: 490-577 (173.7 - 204.6%) -- guaranteed OHKO

252+ SpA Kyogre Water Spout (150 BP) vs. 24 HP / 0 SpD Yveltal in Rain: 456-537 (114.2 - 134.5%) -- guaranteed OHKO

252+ SpA Kyogre Water Spout (150 BP) vs. 252 HP / 252+ SpD Aegislash-Blade in Rain: 486-573 (150 - 176.8%) -- guaranteed OHKO

252+ SpA Kyogre Water Spout (150 BP) vs. 252 HP / 0 SpD Espeon in Rain: 469-553 (140.4 - 165.5%) -- guaranteed OHKO

The only reason you wouldn't run this is because of Primal Groudon. The perfect pairing for this is a Mega-Rayquaza with Earthquake. This ensures the removal of sun and a half life-threatening strike. Even if the Ray dies, the sun is gone ensuring Kyogre can come in and spout it to death.

Use this over primal, always, always, most of the time.