Ok, let's take a look at this team. It looks great, none of the members look like they need replacing. That is... until you consider that literally every member of this team is more physically defensive than specially defensive. I mean, Regirock is your best special tank, and he's not actually supposed to be a special tank. I would advise you to remove one of your Physical tanks (Alomomola, Mudsdale or Regirock) and replace it with a Special tank.
If you opt to replace Alomomola, I would use another Wish passer, like Blissey, or Evolite Chansey. Maybe even Clefable.
If you opt to replace Mudsdale (the weakest link in my opinion), you could use a Specially defensive body press user, like Goodra-H. Possible set:
Goodra-Hisui @ Leftovers
Ability: Shell Armor
Tera Type: Steel
- Acid Armor/Curse
- Body Press
- Heavy Slam
- Earthquake/Draco Meteor/Whatever
If you opt to replace Regirock, Registeel is another option for a rock setter. 80/150/150 defenses aren't bad either. If you want a rocks setter that can check Zard Y, you could use Diance with Diamond Storm.
Calcs for your options:
If you keep Regirock, you don't need 64 Atk. 0 Atk is fine for dealing with Zard Y:
0 Atk Regirock Stone Edge vs. 0 HP / 4 Def Charizard-Mega-Y: 528-624 (177.7 - 210.1%) -- guaranteed OHKO
Watch out for Zard still though:
252 SpA Charizard-Mega-Y Solar Beam vs. 252 HP / 252+ SpD Regirock: 220-260 (60.4 - 71.4%) -- guaranteed 2HKO after Leftovers recovery
Registeel can technically take a hit from Zard Y:
252 SpA Charizard-Mega-Y Weather Ball (100 BP Fire) vs. 252 HP / 252+ SpD Registeel in Sun: 306-362 (84 - 99.4%) -- guaranteed 2HKO after Leftovers recovery
Diance is a possible option as well:
252 SpA Charizard-Mega-Y Solar Beam vs. 252 HP / 252+ SpD Diancie: 164-194 (53.9 - 63.8%) -- guaranteed 2HKO after Leftovers recovery
4 Atk Diancie Diamond Storm vs. 0 HP / 4 Def Charizard-Mega-Y: 532-628 (179.1 - 211.4%) -- guaranteed OHKO
Whichever ones you choose, you need at least one, maybe two special walls. Now, let's look at the rest of the team and add a few tweaks:
Alomomola:
If you choose to keep Alomomola, the set you have is just fine.
Mudsdale:
Mudsdale looks like the weakest of your Physical Walls, and replacing him with Goodra-H is probably the best option. Your team doesn't really need an electric immunity, a specially defensive resist is fine. If you want to keep Mudsdale, put the 12 Atk somewhere else, I did some calcs, and 12 Atk doesn't confirm kills on anything really.
Scizor-Mega:
Looks fine, but the speed EVs don't make sense. You don't really outspeed anything with them. I would put them into Atk, Def, or Spd.
Tapu Koko:
Looks fine, but I notice you don't have a Z-Move user on your team. Tapu Koko is pretty frail anyways, I would get rid of boots and replace with an Electric or Fairy Z-Crystal. The only thing you would need boots for anyways is Sticky Webs, and I think a Z-Crystal would be applicable in more situations.
Regirock:
Looks fine, but get rid of the 64 Atk, like I showed earlier, it's unnecessary. I would put it into Spd. You could also use Diance instead. If you use Diance, you could have your opponent guess which one is your Mega, because both Diance and Scizor can be commonly used without their Mega forms.
Iron Valiant:
All fine, except for Vacuum Wave, it's much weaker than Aura Sphere, and with Quark Drive Speed , you don't need a priority move.
So there you have it. I hope I helped.