Okay, I'll try my best to comment on these Pokemon.
Swellow
This looks fine, but I recommend Adamant over Jolly. The 4 HP should be in SpD probably. Also, Swellow is in RU so it's not exactly fit for National Dex. If you need another good option for Flying-types in National Dex, try Corviknight.
Sample set:
Corviknight @ Leftovers / Rocky Helmet
Ability: Pressure / Mirror Armor
EVs: 252 HP / 184 Def / 72 SpD
Impish Nature
- Defog / Bulk Up
- Body Press / Brave Bird
- U-turn
- Roost
Mienshao
Again, this is a lower tier than OU (NU), but it has seen some usage in UU, so it may be fine. If you don't have any recoil moves, don't use Reckless; it's just useless then. Use Regenerator instead. Choice Scarf and Taunt? Why? Either remove the Scarf or get rid of Taunt. Stone Edge is another good option. Again, I feel the HP EVs should go in SpD, but it doesn't really matter that much. Close Combat is also a better option than High Jump Kick.
Venomoth
I would run Sludge Wave over Sludge Bomb for the extra power, but it doesn't really matter. Sleep Powder is a better option than Psychic, replace it. Probably Defense EVs instead of SpD since you will Quiver Dance anyway, and Venomoth's Defense is kind of lacking. Otherwise, this is fine.
Gothitelle
Hardly ever see Competitive Gothitelle. I would say Leftovers over Iapapa Berry. Consider replacing Competitive with Shadow Tag, as well as something like Taunt, to make Gothitelle perfect for breaking stall.
Slurpuff
This set is, well... weird. Slurpuff's recommended set is:
Slurpuff @ Sitrus Berry
Ability: Unburden
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant / Jolly Nature
- Belly Drum
- Play Rough
- Return
- Drain Punch
This set includes using Unburden + Sitrus Berry + Belly Drum to become faster and stronger than everything, then sweeping. Try this set instead.
Altaria
Since Mega Altaria has the same Physical and Special attack, and its Physical STAB moves are generally stronger, try making this a Physical set instead. Try this set:
Altaria-Mega @ Altarianite
Ability: Pixilate
EVs: 64 HP / 252 Atk / 192 Spe
Adamant Nature
- Return
- Dragon Dance
- Earthquake
- Roost
Thank you for reading. Hope I helped!
