I like the idea of M-Venu. But normal ice coverage P-Ogre can beat it and not lose to P-ogre (freeze dry).Merciless Assault Vest/Safety Goggles Fusion Bolt Zekrom. For when you absolutely, positively want to kill that PH Kyogre dead right now.
+3 252 SpA Kyogre Ice Beam vs. 252 HP / 252 SpD Assault Vest Zekrom: 288-340 (71.2 - 84.1%) -- guaranteed 2HKO
252 Atk Teravolt Zekrom Fusion Bolt vs. 252 HP / 252+ Def Kyogre on a critical hit: 422-498 (104.4 - 123.2%) -- guaranteed OHKO
Fusion Bolt over Bolt Strike for accuracy since you lose if you miss unless Kyo-P isn't boosted. Tricky part is picking AV or Safety Goggles since one lets you deal with a few Q.Dances and one lets you evade the Spore. You can then run moves like Low Kick for PH Gigas and Dragon Hammer for PH Giratina.
Also worth noting is the forgotten Mega-Venusaur checks Pogre nicely. It resists Water/Fairy sets and is immune to both Spore and Leech Seed. Additionally, it can do the old Black Sludge trick to cripple Pogre while getting a Toxic Orb to toss at another Pokemon later without fearing a Toxic status. Run Prankster with Topsy and all you have to do is not switch into an Ice Beam. And if they are running Ice Beam over Moonblast, then the Pogre will likely lose to Pogres that are running Moonblast. Or it could run three attacks, but a big reason of why Pogre is a pain is Spore/Leech Seed give it lots of chances to set-up while making it all but fully imposter proof, especially if not running Water Spout since that risks losing a speed tie and getting crit OHKOed after a few Q.Dances, so it actually loses a bit of threat doing that.
Funny enough though, this is actually the first time we've have P.Ogre without EV limit.
I think the best set for using M-Venu is unaware:
Venusaur-Mega @ Black Sludge
Ability: Unaware
EVs: 252 HP / 252 Def / 252 SpA / 252 SpD / 252 Spe
Calm Nature
- Thousand Waves
- Giga Drain / Leech seed
- Entrainment
- Shore Up
252 SpA Kyogre-Primal Freeze-Dry vs. 252 HP / 252+ SpD Venusaur-Mega: 124-148 (34 - 40.6%) -- 53.2% chance to 3HKO after Black Sludge recovery
It's not a perfect check... But I can see it working in some circumstances.