252 Atk Choice Band Adaptability Mamoswine Earthquake vs. +1 252 HP / 252+ Def Snorlax: 206-244 (39.3 - 46.5%) -- guaranteed 3HKO after Leftovers recovery(again, worse case scenario,although physically defensive curselax is actually really amazing)
252 Atk Choice Band Adaptability Mamoswine Earthquake vs. 252 HP / 252+ Def Suicune: 214-254 (52.9 - 62.8%) -- 99.6% chance to 2HKO after Leftovers recovery\
252 Atk Choice Band Adaptability Mamoswine Icicle Crash vs. 252 HP / 252+ Def Zapdos: 224-264 (58.3 - 68.7%) -- guaranteed 2HKO after Leftovers recovery(changed to pure electric for "delta stream")
Snorlax:
252 Atk Choice Band Adaptability Mamoswine Earthquake vs. +1 252 HP / 252+ Def Snorlax: 206-244 (39.3 - 46.5%) -- 85.2% chance to 3HKO after Poison Heal
+1 0- Atk Snorlax Facade (140 BP) vs. 0 HP / 0 Def Mamoswine: 265-313 (73.8 - 87.1%) -- guaranteed 2HKO
Suicune:
252 Atk Choice Band Adaptability Mamoswine Earthquake vs. 252 HP / 252+ Def Suicune: 214-254 (52.9 - 62.8%) -- 80.1% chance to 2HKO after Poison Heal
4 SpA Suicune Scald vs. 0 HP / 0- SpD Mamoswine: 270-318 (75.2 - 88.5%) -- guaranteed 2HKO
Zapdos:
252 Atk Choice Band Adaptability Mamoswine Icicle Crash vs. 252 HP / 0+ Def Zapdos in Strong Winds: 288-340 (75 - 88.5%) -- guaranteed 2HKO after Leftovers recovery
252 SpA Zapdos Heat Wave vs. 0 HP / 0- SpD Mamoswine: 340-400 (94.7 - 111.4%) -- 68.8% chance to OHKO
Just want to point out that three of your calculations are misleading. Two check Mamo while Zapdos checks it 70% of the time. Factor in Rocks and Zapdos also checks it reliably.
Not to mention, I don't see why you're listing Hippo here. Of course Mamoswine 2HKOs it as it is weak to ice. Even Refrigerate Sneasel 2HKOs it. Or so do most ice types in the game.
-1 252 Atk Life Orb Refrigerate Sneasel Double-Edge vs. 252 HP / 252+ Def Hippowdon: 229-273 (54.5 - 65%) -- guaranteed 2HKO after Leftovers recovery
Also, here's a nice counter for you:
Intimidate Mega-Slowbro:
-1 252 Atk Choice Band Mamoswine Knock Off vs. 252 HP / 252+ Def Slowbro: 96-114 (24.3 - 28.9%) -- 99.5% chance to 4HKO
4 SpA Slowbro Scald vs. 0 HP / 0+ SpD Mamoswine: 240-284 (66.8 - 79.1%) -- guaranteed 2HKO
You can use Slack Off to shake off any damage and you don't need to Mega Evolve immediately either. If you do,
-1 252+ Atk Choice Band Adaptability Mamoswine Earthquake vs. 252 HP / 252+ Def Mega Slowbro: 112-134 (28.4 - 34%) -- 1.1% chance to 3HKO
-1 252+ Atk Choice Band Mamoswine Knock Off vs. 252 HP / 252+ Def Mega Slowbro: 74-88 (18.7 - 22.3%) -- possible 5HKO
4 SpA Mega Slowbro Scald vs. 0 HP / 0 SpD Mamoswine: 326-386 (90.8 - 107.5%) -- 43.8% chance to OHKO