This is my first time creating a team ever, and I'm not that familiar with the meta for gen 8 but here goes nothing. Also before I present the team, I'd like to just preface that this is a rain composition.
Barraskewda @ Choice Band
Ability: Swift Swim
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- Aqua Jet
- Waterfall
- Poison Jab
- Drill Run
Swift swim and the high attack damage makes it so Barraskewda will assassinate anything it encounters. Any water type Pokémon will counter Barraskewda, thus a potential sweep could only occur after I get rid of any water type switch-ins. Additionally, common threats in the tier such as Ferrothorn, Tapu Koko, Regieleki, and even Landorus-therian will most likely either have to be weakened greatly or taken out by the time I switch in Barraskewda.
Pelipper @ Damp Rock
Ability: Drizzle
EVs: 252 HP / 252 Def / 4 Spa
Bold Nature
- U-turn
- Scald
- Roost
- Defog
Pelipper is key for the entire team composition to operate as it is meant to set up the rain with Drizzle and Damp Rock. Additionally, since I have 2 flying types and many moves that switch in and out pokemon (u-turn, volt switch), its imperative that Pelipper serves as the defogger of the team in order to protect my frequent switches. Finally, I maxed out phys defense EVs and added roost and scald are meant to wall physically offensive Pokémon.
Amoonguss @ Black Sludge
Ability: Regenerator
EVs: 252 HP / 67 SpA / 189 SpD
Gentle Nature
- Giga Drain
- Clear Smog
- Spore
- Protect
Amoonguss is meant to provide coverage against the one OU Pokémon I don't have coverage for on this team being Swampert. Additionally Amoonguss will serve as a special wall and clear smog will prevent any cm sweeps. Finally, since I have coverage for all of its type counters, amoonguss will always serve as a potential switch in with regenerator ensuring its safety.
Zapdos @ Choice Specs
Ability: Static
EVs: 252 SpA / 252 Spe / 4HP
Timid Nature
- Volt Switch
- Extrasensory
- Thunder
- Hurricane
Zapdos will serve as one of the wall breakers with strong stab coverage for grass counters on my water types and more importantly, coverage against opposing water types that might seek to take advantage of the rain. Additionally extrasensory would provide coverage against good switch-ins such as lucario, which could is a good pivot against most of my team since it provides type coverage with decent offensive stats. Finally, Thunder and Hurricane have good synergy with the rain setup as they have extremely strong base damage that can be paired up with 100% accuracy under the rain.
Excadrill @ Air Balloon
Ability: Sand Rush
EVs: 252 Atk / 252 Spe / 4HP
Jolly Nature
- Iron Head
- Earthquake
- Rock slide
- Stealth Rock
Excadrill serves to set up rocks for the team as well as provide as a strong pivot against many threats against my team namely the electric types. Additionally, rock slide would provide good coverage against ice types which are a big threat to my team. Finally, since I'm running air balloon, until the air balloon pops, Excadrill's only type weakness would be fighting types which would give good pivot potential against clerics and walls.
Kingdra @ Choice Specs
Ability: Swift Swim
EVs: 252 SpA / 252 Spe / 4HP
Modest Nature
- Ice Beam
- Draco Meteor
- Hydro Pump
-flash cannon
Kingdra is mean to serve as the swift swim spA sweeper. The ice beam also provides coverage against ice types that Barraskewda can't cover and the flash cannon provide coverage against its only type weakness being fairy types. Kingdra is also a good check to dragon types which could potentially shut down my rain composition due to resisting water stab from Barraskewda and Pelipper.
Barraskewda @ Choice Band
Ability: Swift Swim
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- Aqua Jet
- Waterfall
- Poison Jab
- Drill Run
Swift swim and the high attack damage makes it so Barraskewda will assassinate anything it encounters. Any water type Pokémon will counter Barraskewda, thus a potential sweep could only occur after I get rid of any water type switch-ins. Additionally, common threats in the tier such as Ferrothorn, Tapu Koko, Regieleki, and even Landorus-therian will most likely either have to be weakened greatly or taken out by the time I switch in Barraskewda.
Pelipper @ Damp Rock
Ability: Drizzle
EVs: 252 HP / 252 Def / 4 Spa
Bold Nature
- U-turn
- Scald
- Roost
- Defog
Pelipper is key for the entire team composition to operate as it is meant to set up the rain with Drizzle and Damp Rock. Additionally, since I have 2 flying types and many moves that switch in and out pokemon (u-turn, volt switch), its imperative that Pelipper serves as the defogger of the team in order to protect my frequent switches. Finally, I maxed out phys defense EVs and added roost and scald are meant to wall physically offensive Pokémon.
Amoonguss @ Black Sludge
Ability: Regenerator
EVs: 252 HP / 67 SpA / 189 SpD
Gentle Nature
- Giga Drain
- Clear Smog
- Spore
- Protect
Amoonguss is meant to provide coverage against the one OU Pokémon I don't have coverage for on this team being Swampert. Additionally Amoonguss will serve as a special wall and clear smog will prevent any cm sweeps. Finally, since I have coverage for all of its type counters, amoonguss will always serve as a potential switch in with regenerator ensuring its safety.
Zapdos @ Choice Specs
Ability: Static
EVs: 252 SpA / 252 Spe / 4HP
Timid Nature
- Volt Switch
- Extrasensory
- Thunder
- Hurricane
Zapdos will serve as one of the wall breakers with strong stab coverage for grass counters on my water types and more importantly, coverage against opposing water types that might seek to take advantage of the rain. Additionally extrasensory would provide coverage against good switch-ins such as lucario, which could is a good pivot against most of my team since it provides type coverage with decent offensive stats. Finally, Thunder and Hurricane have good synergy with the rain setup as they have extremely strong base damage that can be paired up with 100% accuracy under the rain.
Excadrill @ Air Balloon
Ability: Sand Rush
EVs: 252 Atk / 252 Spe / 4HP
Jolly Nature
- Iron Head
- Earthquake
- Rock slide
- Stealth Rock
Excadrill serves to set up rocks for the team as well as provide as a strong pivot against many threats against my team namely the electric types. Additionally, rock slide would provide good coverage against ice types which are a big threat to my team. Finally, since I'm running air balloon, until the air balloon pops, Excadrill's only type weakness would be fighting types which would give good pivot potential against clerics and walls.
Kingdra @ Choice Specs
Ability: Swift Swim
EVs: 252 SpA / 252 Spe / 4HP
Modest Nature
- Ice Beam
- Draco Meteor
- Hydro Pump
-flash cannon
Kingdra is mean to serve as the swift swim spA sweeper. The ice beam also provides coverage against ice types that Barraskewda can't cover and the flash cannon provide coverage against its only type weakness being fairy types. Kingdra is also a good check to dragon types which could potentially shut down my rain composition due to resisting water stab from Barraskewda and Pelipper.
with 
. This is non negotiable. Ferrothorn has been a rain staple since forever and for good reason. It's main job is to be a buffer against Rillaboom. Yes, a buffer because this thing loses to any non banded Rillaboom. More importantly, it has spikes, which would quickly wear down any grounded enemies along with a million annoying moves this mon has
with 
. Swampert serves as your special buffer with a switch move along with key resistances to rock and electric to ensure Ferrothorn cannot be easily overwhelmed. It can also annoy one of rain's hated, yet rare, enemy, Rotom Wash. Perhaps the most important part is that it has stealth rock, opening up a moveslot on Ferrothorn. Rocks + spikes takes a quarter of your opponent's hp if they are neutral to rocks. Others would usually recommend Seismitoad here but I don't see the need otherwise you will be hard pressed to keep up the rain or your team will just be outsped and destroyed
This ensures that you don't die to the fourth stealth rock switch in and live on one hp
on 
. You wouldn't believe how easily this mon dies without boots. You can then replace its moveset with rain reliant stabs, roost and weather ball
, replace flash cannon with surf. You don't want to rely on hydro pump if you wanna use Kingdra to sweep. This way, it can use hydro pump if it needs to be a wallbreaker or surf if it needs to be a sweeper