Freeze-Dry Life Orb Mamoswine, if already out destroys this core by itself with Freeze-Dry, Earthquake, and the killing Ice Shard which prevents either from easily switching in. Another threat would be Life Orb 3 attack Roost Kyurem-Black who has the tools to destroy Mega Sceptile (with ice beam) and Azumarill with fusion bolt (which if low enough kills Mega-Sceptile due to Teravolt) once it gets in on a predicted waterfall/aqua jet. If Kyurem-Black is facing Mega Sceptile 1v1 dragon pulse fails to Kill without prior damage and it has to be wary of scarf variants of Kyurem-Black which has risen in popularity as of late.
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Mamoswine @ Life Orb
Ability: Thick Fat
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Ice Shard
- Earthquake
- Icicle Crash
- Knock Off
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Kyurem-Black @ Life Orb
Ability: Teravolt
EVs: 20 Atk / 252 SpA / 236 Spe
Mild Nature
- Ice Beam
- Earth Power
- Fusion Bolt
- Roost
-244 Atk Life Orb Mamoswine Earthquake vs. 52 HP / 0 Def Azumarill: 255-302 (72 - 85.3%) -- guaranteed 2HKO
-244 Atk Life Orb Mamoswine Ice Shard vs. 52 HP / 0 Def Azumarill: 51-61 (14.4 - 17.2%) -- possible 6HKO
-12 SpA Life Orb Mamoswine Freeze-Dry vs. 52 HP / 0 SpD Azumarill: 179-213 (50.5 - 60.1%) -- guaranteed 2HKO
244 Atk Life Orb Mamoswine Ice Shard vs. 0 HP / 4 Def Mega Sceptile: 437-515 (155.5 - 183.2%) -- guaranteed OHKO
252 SpA Mega Sceptile Dragon Pulse vs. 0 HP / 0- SpD Mamoswine: 255-300 (71 - 83.5%) -- guaranteed 2HKO
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252 SpA Mega Sceptile Dragon Pulse vs. 0 HP / 0 SpD Kyurem-B: 330-390 (84.3 - 99.7%) -- guaranteed 2HKO
252+ SpA Life Orb Teravolt Kyurem-B Ice Beam vs. 0 HP / 0- SpD Mega Sceptile: 1014-1201 (360.8 - 427.4%) -- guaranteed OHKO
252+ Atk Choice Band Huge Power Azumarill Aqua Jet vs. 0 HP / 0- Def Kyurem-B: 66-78 (16.8 - 19.9%) -- guaranteed 6HKO
56 Atk Life Orb Teravolt Kyurem-B Fusion Bolt vs. 52 HP / 0 Def Azumarill: 372-439 (105 - 124%) -- guaranteed OHKO
I don't think this is what we are looking for.
As you yourself mentioned in the calculations, Mamo's EQ doesn't KO Azumarill who OHKOes back with Waterfall. Kyurem-B gets hit very hard by Dragon Pulse such that any prior damage, say Stealth Rock or Banded Aqua Jet will finish it off.