Marshadow:

252+ Atk Life Orb Marshadow Close Combat vs. 252 HP / 252+ Def Eviolite Chansey: 720-850 (102.2 - 120.7%) -- guaranteed OHKO
(Although, Chansey usually runs SpD)

252+ Atk Life Orb Marshadow Close Combat vs. 4 HP / 252 Def Blissey: 1079-1271 (165.4 - 194.9%) -- guaranteed OHKO

252+ Atk Life Orb Marshadow Close Combat vs. 0 HP / 0 Def Kyurem-White: 595-702 (152.1 - 179.5%) -- guaranteed OHKO

252+ Atk Life Orb Marshadow Close Combat vs. 252 HP / 4 Def Ferrothorn: 432-510 (122.7 - 144.8%) -- guaranteed OHKO

252+ Atk Life Orb Marshadow Poltergeist (110 BP) vs. 252 HP / 0 Def Eternatus: 261-308 (53.9 - 63.6%) -- guaranteed 2HKO after Black Sludge recovery

252+ Atk Life Orb Marshadow Close Combat vs. 252 HP / 4 Def Gastrodon: 372-438 (87.3 - 102.8%) -- 18.8% chance to OHKO

252+ Atk Life Orb Marshadow Poltergeist (110 BP) vs. 252 HP / 252+ Def Prism Armor Necrozma-Dusk-Mane: 230-271 (57.7 - 68%) -- guaranteed 2HKO

Kyogre:

252 SpA Choice Specs Kyogre Water Spout (150 BP) vs. 252 HP / 4 SpD Necrozma-Dusk-Mane in Rain: 567-667 (142.4 - 167.5%) -- guaranteed OHKO

252 SpA Choice Specs Kyogre Water Spout (150 BP) vs. 252 HP / 4 SpD Shadow Shield Lunala in Rain: 288-339 (60.2 - 70.9%) -- guaranteed 2HKO

252 SpA Choice Specs Kyogre Ice Beam vs. 252 HP / 0 SpD Zygarde-Complete: 684-808 (107.5 - 127%) -- guaranteed OHKO

252 SpA Choice Specs Kyogre Water Spout (150 BP) vs. 252 HP / 252+ SpD Yveltal in Rain: 447-526 (98 - 115.3%) -- 87.5% chance to OHKO

252 SpA Choice Specs Kyogre Water Spout (150 BP) vs. 252 HP / 4 SpD Quagsire in Rain: 865-1018 (219.5 - 258.3%) -- guaranteed OHKO

252 SpA Choice Specs Kyogre Water Spout (150 BP) vs. 252 HP / 252+ SpD Tyranitar in Sand: 392-464 (97 - 114.8%) -- 81.3% chance to OHKO

252 SpA Choice Specs Kyogre Thunder vs. 252 HP / 4 SpD Toxapex: 294-348 (96.7 - 114.4%) -- 81.3% chance to OHKO

252 SpA Choice Specs Kyogre Ice Beam vs. 248 HP / 40 SpD Giratina: 272-320 (54 - 63.6%) -- guaranteed 2HKO after Leftovers recovery

252 SpA Choice Specs Kyogre Water Spout (150 BP) vs. 248 HP / 52 SpD Ho-Oh in Rain: 812-956 (195.6 - 230.3%) -- guaranteed OHKO