So assuming I've already accrued a KO with Magearna, this is the best you can do with +1 All-Out Pummeling.
+1 252+ SpA Magearna All-Out Pummeling vs. 252 HP / 252+ SpD Celesteela: 243-286 (61 - 71.8%) -- guaranteed 2HKO
Thunderbolt is looking a little more viable now, since it also beats Toxapex which otherwise walls you. +1 Thunderbolt 2HKOs Celesteela on its own, and with pretty much any prior damage and Rocks, +1 LO Thunderbolt KOs.
+1 252+ SpA Life Orb Magearna Thunderbolt vs. 252 HP / 252+ SpD Celesteela: 299-354 (75.1 - 88.9%) -- 6.3% chance to OHKO after Stealth Rock
+1 252+ SpA Life Orb Magearna Thunderbolt vs. 252 HP / 252+ SpD Toxapex: 237-281 (77.9 - 92.4%) -- 31.3% chance to OHKO after Stealth Rock
I think I'm gonna keep running Bisharp or other Pursuit mons with Magearna and Koko. Shutting down Marowak that easily is pretty cash.
+1 252+ SpA Magearna All-Out Pummeling vs. 252 HP / 252+ SpD Celesteela: 243-286 (61 - 71.8%) -- guaranteed 2HKO
Thunderbolt is looking a little more viable now, since it also beats Toxapex which otherwise walls you. +1 Thunderbolt 2HKOs Celesteela on its own, and with pretty much any prior damage and Rocks, +1 LO Thunderbolt KOs.
+1 252+ SpA Life Orb Magearna Thunderbolt vs. 252 HP / 252+ SpD Celesteela: 299-354 (75.1 - 88.9%) -- 6.3% chance to OHKO after Stealth Rock
+1 252+ SpA Life Orb Magearna Thunderbolt vs. 252 HP / 252+ SpD Toxapex: 237-281 (77.9 - 92.4%) -- 31.3% chance to OHKO after Stealth Rock
I think I'm gonna keep running Bisharp or other Pursuit mons with Magearna and Koko. Shutting down Marowak that easily is pretty cash.