Haunter @ Life Orb
EVs: 252 SpA / 4 SpD / 252 Spe
- Sludge Wave
- Shadow Ball
- Reflect Type
Haunter outspeeds even Jolly Zangoose, is immune to Quick Attack, and OHKOs it with Sludge Wave after either a Belly Drum or Stealth Rock damage. It can't be brought in Knock Off, however, as it OHKOs, +6 or not.
252 SpA Life Orb Haunter Sludge Wave vs. 0 HP / 4 SpD Zangoose: 278-329 (96.8 - 114.6%) -- 81.3% chance to OHKO
252+ Atk Zangoose Knock Off (97.5 BP) vs. 0 HP / 0 Def Haunter: 398-470 (172.2 - 203.4%) -- guaranteed OHKO
Alolan Persian is a decent check to BD Zangoose for several reason I've found.
Persian's speed tier means that it needs hardly any investment to outspeed Adamant Zangoose. I chose this specific spread because it still outspeeds max base 100s.
If they are both in on the same turn Persian can Taunt Zangoose to keep it from setting up a Belly Drum. Even if they predict the Taunt, Persian can eat an unboosted Close Combat and KO the next turn with Foul Play.
If Persian switches into a Zangoose on the turn it Belly Drums, it can easily live a +6 Quick Attack and beat it with Foul Play. And if they decide not to Quick Attack then as stated above, you outspeed them and KO.
Also an option, you can run a spread of 252HP / 200Def / 56Spe to specifically target Zangoose and live two Quick Attacks but outside of that, it has little use.
252+ Atk Zangoose Close Combat vs. 252 HP / 120 Def Fur Coat Persian-Alola: 168-198 (50.2 - 59.2%) -- guaranteed 2HKO
+6 252+ Atk Zangoose Quick Attack vs. 252 HP / 120 Def Fur Coat Persian-Alola: 168-198 (50.2 - 59.2%) -- guaranteed 2HKO
0 Atk Persian-Alola Foul Play vs. 4 HP / 0 Def Zangoose: 237-279 (82.2 - 96.8%) -- guaranteed 2HKO
0 Atk Persian-Alola Foul Play vs. -1 4 HP / 0 Def Zangoose: 354-417 (122.9 - 144.7%) -- guaranteed OHKO (after CC drop)
+6 0 Atk Persian-Alola Foul Play vs. 4 HP / 0 Def Zangoose: 943-1110 (327.4 - 385.4%) -- guaranteed OHKO
I honestly don't know what I could consider this since there could be valid arguments for both, but I'll sit this here as a check for now. Could change it if needed be. If Shiinotic is in a straight up 1v1 situation, Shiinotic can either Spore the Zangoose on the Belly Drum turn and proceed to 2HKO Zangoose with Moonblast. In a more realistic situation where Shiinotic is switching in on the Belly Drum turn (or something dies and you switch Shiinotic into a +6 Zangoose after the sac), Shiinotic easily tanks its hits and can heal back to full HP multiple turns due to Zangoose's high attack and Strength Sap. Over time, Zangoose hits begins to get weaker due to Strength Sap lowering its attack and it can hit Zangoose when its safe to while being able to heal back up safely against other Pokemon. Effect Spore is also nice as all of Zangoose's attacks makes contact so getting a status off on it is really good too.
+6 252 Atk Zangoose Quick Attack vs. 252 HP / 252+ Def Shiinotic: 199-235 (61.4 - 72.5%) -- guaranteed 2HKO after Leftovers recovery
4 SpA Shiinotic Moonblast vs. 0 HP / 0 SpD Zangoose: 144-169 (50.1 - 58.8%) -- guaranteed 2HKO
Sableye @ Leftovers
EVs: 248 HP / 252 Def / 8 SpD
- Knock Off
Prankster and immunity to everything except Knock Off makes Sableye a pretty decent check counter. Priority Taunt stops Zang from drumming. Even if it's already drummed, Sableye survives Knock Off after the priority burn. All subsequent Knock Off hits do less than 50%, so you can just recover until it's dead or you feel comfortable enough to retaliate with your own Knock Off.
Even if for some reason you've let Sabeleye get worn down prior to Zangoose dropping or it gets a lucky crit, the burn effectively neuters the mon so that anything decently bulky can finish it off.
+6 252+ Atk burned Zangoose Knock Off (97.5 BP) vs. 248 HP / 252+ Def Sableye: 183-216 (60.3 - 71.2%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
+6 252+ Atk burned Zangoose Knock Off vs. 248 HP / 252+ Def Sableye: 123-145 (40.5 - 47.8%) -- guaranteed 3HKO