Battle Stadium Series 2 Role Compendium
Here, we'll be doing some light analyses on common and uncommon roles in the metagame, and listing some Pokemon for you to use in said role!
Since things are early for the Series 2 metagame, we won't really divide roles on viability yet beyond what made sense in Series 1. Once things become more clear, we'll divide things into viability too!
ALSO: THIS IS NOT FINISHED YET! THIS IS JUST WHAT WE GOT SO FAR!
Hazards
Stealth Rock
Even in the fast paced world of 3v3, Stealth Rock can make plenty of sense on a team. While setting them up every game isn't a must, they're a huge help against Focus Sash foes and Dragonite alike.
Defensive Stealth Rock Setters
These Pokemon are bulky options that are pretty reliable at getting Stealth Rock up, and even support in other ways.
Likely to be major

Hippowdon

Garchomp

Annihilape

Great Tusk

Clodsire

Tinkaton

Garganacl
Likely to be viable

Iron Treads

Scream Tail

Torkoal
Likely to be niche

Chansey

Tyranitar

Dudunsparce

Orthworm

Mudsdale

Gastrodon

Krookodile
Offensive Stealth Rock Setters
These Pokemon often try to get Stealth Rock up by ANY means necessary, with many of them even using Focus Sash to guarantee it!
Likely to be major

Great Tusk

Garchomp

Glimmora
Likely to be viable

Hydreigon

Kingambit
Likely to be niche

Sandy Shocks

Iron Thorns

Lycanroc-D
Toxic Spikes
Toxic Spikes aren't really too common, and the good absorbers can make it tricky to use. However, it can be devestating against the right match-up, and the Pokemon that use them can do more than just that anyways! You got two categories: Defensive ones, and Offensive ones who just have the option of using Toxic Spikes (but don't always run it). And of course..
Toxic Debris Setter (duh)

Glimmora
Defensive Toxic Spikes Setters
Likely to be major

Clodsire
Likely to be niche

Toxapex
Offensive Toxic Spikes Setters
Likely to be viable

Iron Moth

Meowscarada
Likely to be niche

Gengar

Pincurchin
Spikes
Traditionally, Spikes have been a very rare hazard in Battle Stadium Singles, since they take time to be as effective compared to Stealth Rock, which can be a liability in a 3v3 environment. However, with the rise of Spikes Garchomp, clearly they have worth this generation! Generally, being able to use Stealth Rock as well is prefered, because Stealth Rock + Spikes do a lot of damage together!
The Big One

Garchomp
Other potential, less common users

Clodsire

Glimmora
Likely to be niche

Orthworm

Sandy Shocks

Iron Thorns
Rapid Spin
Back in previous generations, Rapid Spin used to be considered a waste of time, due to the fast paced nature of 3v3. However, with the rise of Spikes Garchomp, and the sheer power of Multiscale Dragonite, Rapid Spin is not as useless as it used to be! Don't expect it to be common, but it's something to keep in mind.
Likely to be major

Great Tusk
Likely to be viable

Iron Treads

Torkoal

Glimmora (Mortal Spin)
Sticky Web
On paper, Sticky Web sounds like it could be quite powerful this generation.., but the distribution is NOT good right now. This is listed more out of obligation than something to prepare for. So if you really want to use Sticky Webs, these are your only options...
The one that might be usable?

Masquerain
Your other sad choices

Spidops

Kricketune
Status, Disruption, and Debuffs
Sleep
Since Battle Stadium Singles does not have Sleep Clause, this is an extremely powerful status!
Spore
It doesn't get much better than Spore, with its wonderful 100% accuracy!

Breloom

Amoonguss

Brute Bonnet
Yawn
Yawn's extra turn doesn't make it great at instant gratification, but its great at forcing switches and its wide learnpool makes it a major move!
Likely to be major

Hippowdon

Dondozo

Skeledirge

Umbreon

Sylveon
Likely to be viable

Torkoal

Clodsire
Likely to be niche

Slowking

Slowbro

Dudunsparce

Houndstone
Hypnosis
The 60% accuracy makes Hypnosis a very risky move, but the speedy Pokemon that can viably use it can be devestating if the lady luck is on their side!

Espathra

Iron Valiant

Gengar
Paralysis
Paralysis is a powerful speed control option that can last the whole match, and it has a fairly wide variety of viable users too!
Thunder Wave
Likely to be major

Dragonite

Gholdengo

Tinkaton
Likely to be viable

Scream Tail

Flutter Mane

Hydreigon

Gengar

Dragapult

Kingambit

Mimikyu

Umbreon

Grimmsnarl

Blissey

Chansey
Likely to be niche

Bellibolt

Gyarados

Pincurchin

Sandy Shocks

Tyranitar
Glare
Not only is Glare more accurate than Thunder Wave, but it hits Ground-types too! But it has a very poor distribution...
The one good Glare user

Dudunsparce
Nuzzle
Since this is an attack, it can break Focus Sash and ignore Taunt! Nuzzle also has a very small distribution, though.
The major user

Pawmot
Other likely very niche users

Toxtricity

Hatterene
Fling + Light Ball
Pikachu? Nah that thing sucks, the real use of Light Ball is to Fling it on foes, paralyzing Ground-types and Gholdengo! Note that Covert Cloak does block this effect though.
Likely to use it

Annihilape

Blissey
Likely to be niche

Garchomp

Garganacl

Krookodile
Burn
Burns are somewhat risky to attempt inflicting since there isn't a 100% reliable way to do so, but halving Attack is so strong that it's worth considering!
Will-O-Wisp
The one status move to inflict burn, though the 85% accuracy can be annoying...
Likely to be major

Skeledirge

Volcarona

Dragapult

Rotom-W
Likely to be viable

Mimikyu

Paldean Tauros-Fire

Slither Wing

Rotom-H
Likely to be niche

Gengar

Ceruledge

Torkoal

Houndstone

Arcanine
Fling + Flame Orb
This is a pretty rare combo, but it does give a few Pokemon a highly unexpected way to burn stuff!

Garganacl

Blissey
Toxic Poisoning
This is a status that wears down foes like no other, but it's extremely limited distribution still makes it rather uncommon.
Toxic
Likely to use it

Clodsire

Toxapex
Unlikely to use it often

Gengar

Glimmora
Fling + Toxic Orb / Poison Barb
Now this is a real rarity, but Fling + Toxic Orb DOES get some surprising status (or Poison Barb if you want regular poison in exchange for not getting status'd lol)

Garganacl

Blissey
Ghost-type Curse
Cutting half your health might make Curse seem like an iffy move on Ghost-types, but it deals so much chip damage it can be worth it, especially if you're trying to sack your Pokemon anyways!
Likely to be major

Mimikyu

Dragapult

Annihilape
Likely to be niche

Skeledirge

Tera Ghost Garganacl

Gengar
Leech Seed
Leech Seed has been an annoying status in the past, but the biggest users of it got smacked by dexit this gen.
Most likely to sometimes use it.

Meowscarada
Uncommon Pokemon that might use it

Scovillain

Arboliva
Taunt
The ability to shut down defense and support Pokemon makes Taunt very valuable!
Likely to be major

Annihilape

Corviknight

Meowscarada
Likely to be viable

Flutter Mane

Roaring Moon

Great Tusk

Iron Bundle

Iron Valiant

Kingambit

Mimikyu

Umbreon

Ceruledge

Gengar

Quaquaval

Hydreigon
Likely to be niche

Tyranitar

Iron Thorns

Gyarados

Krookodile
Encore
Encore has proven itself to be a fairly debilitating move, so be prepared for it!
Likely to be major

Dragonite

Iron Bundle

Scream Tail

Tinkaton
Likely to be viable

Skeledirge

Iron Valiant

Annihilape

Gengar

Quaquaval

Pawmot
Likely to be niche

Sableye

Grafaiai
Trick / Switcheroo
Choice Trick / Switcheroo
This is the bane of defensive Pokemon everywhere!
Likely to be major

Gholdengo

Iron Valiant

Rotom-W

Rotom-H

Mimikyu

Meowscarada
Likely to be niche

Grimmsnarl

Gengar

Scream Tail

Armarouge

Slowking

Slowbro

Houndstone
Trick + Lagging Tail
This rather rare strategy is an interesting alternative to paralysis.

Gholdengo

Blissey

Grimmsnarl

Slowking
Knock Off
Besides being a pretty powerful move, this rare treat is great at removing important items!
Likely to be major

Meowscarada

Great Tusk

Iron Treads

Iron Valiant

Tinkaton
Likely to be niche

Cyclizar
Trapping
Removing the ability to switch is quite powerful! However, the current ways of doing so are a bit limited outside of a few major options.
Trapping Moves
Likely to be major

Dragonite (Fire Spin)
Likely to be viable

Roaring Moon (Jaw Lock + Shed Shell)
Trapping Abilities
You'd think trapping abilities would be REALLY scary, and they are... but the selection is rather limited this generation.
Likely to be niche

Gothitelle (Shadow Tag)

Magnezone (Magnet Pull)
Likely to be VERY rare

Dugtrio (Arena Trap)
Disable
While not common, Disable can be horrifying against Choiced Pokemon, and in general is particularly effective at taking control of a foe.
Likely to be major

Dragapult
Likely to be viable

Scream Tail
Likely to be niche

Iron Valiant

Gengar

Sableye
Cursed Body

Gengar

Dual Screens Dragapult
Speed Debuffs
In the fast paced world of 3v3 battles, speed control attacks can be quite useful!
Likely to be major

Annihilape (Bulldoze, Rock Tomb, Low Sweep)

Breloom (Bulldoze, Rock Tomb)

Glimmora (Mud Shot)
Likely to be viable

Garchomp (Bulldoze, Rock Tomb)

Paldean Tauros-Fire (Rock Tomb)

Hippowdon (Rock Tomb)
Offensive Debuffs
These aren't terribly common, but some Pokemon have good reasons for using it!
Intimidate
This is by far the easiest way to debuff physical attack, even if the selection is not as good as you'd hope right now.
Likely to be viable

Salamence

Paldean Tauros-Fire
Likely to be niche

Gyarados

Paldean Tauros-Water

Krookodile
Chilling Water
This isn't a terribly common move, but it sees a bit of use

Toxapex

Bellibolt
Memento
This is a move to use if you are willing to go all-in on a specific set up for another Pokemon!
Likely to be viable

Glimmora

Gholdengo
Likely to be niche

Pincurchin

Rabsca
Defensive Debuffs
This is not something you'll see a lot of, but there is one interesting example to note!
Acid Spray
Acid Spray won't help you sweep like say, Nasty Plot would, but its secret is that Unaware walls don't really like facing this move!
Likely to be viable

Iron Moth
Likely to be niche

Bellibolt
Stat Removal
These aren't particularly common, but Clear Smog and Haze are good options for the few defensive Pokemon that get them!
Clear Smog

Amoonguss
Haze

Toxapex
Offensive Roles
1-turn Set-up Sweepers
This is exactly what it says on the tin: these are very offensive Pokemon that only need one turn of set up to sweep! Note that some of these Pokemon can actually be bulky sweepers as well.
Speed Boosting
Since these boosts tend to be a bit lighter on the offensive side, a lot of these tend to be more late game sweepers than something you see breaking walls.
Likely to be major
Dragon Dance: 
Dragonite

Baxcalibur

Dragapult

Roaring Moon
Quiver Dance: 
Volcarona
Booster Energy: 
Flutter Mane

Iron Valiant

Roaring Moon
Likely to be viable
Dragon Dance: 
Salamence
Speed Boost: 
Calm Mind Espathra
Shell Smash: 
Cloyster
Speed Boosting Attack: 
Rapid Spin Great Tusk

Moxie Quaquaval

Trailblaze Brute Bonnet
Likely to be niche
Dragon Dance: 
Gyarados

Tyranitar

Iron Thorns

Haxorus
Weak Armor: 
Ceruledge

Armarouge
Booster Energy: 
Iron Jugulis
Mainly Offensive Boosting
Likely to be major
Swords Dance: 
Garchomp

Kingambit

Mimikyu

Iron Valiant

Baxcalibur
Nasty Plot: 
Gholdengo

Rotom-W
Bulk Up: 
Great Tusk
Calm Mind: 
Flutter Mane
Likely to be viable
Swords Dance:
Scizor

Breloom

Quaquaval

Iron Hands
Nasty Plot: 
Hydreigon
Bulk Up: 
Slither Wing
Calm Mind: 
Iron Valiant

Espathra

Sylveon
Likely to be niche
Swords Dance: 
Ceruledge

Tinkaton

Gallade

Haxorus
Nasty Plot: 
Gengar
Bulk Up / Coil: 
Paldean Tauros-Fire

Paldean Tauros-Water

Dudunsparce
Calm Mind: 
Armarouge

Dudunsparce
Work Up: 
Iron Jugulis
Bulky Sweepers
These Pokemon take the tortoise's side: slow and steady set-ups win the race! These Pokemon usually aim to get multiple boosts before they attempt to sweep, thanks to major bulk investment.
Likely to be major
Bulk Up: 
Annihilape

Great Tusk
Curse: 
Dondozo
Dragon Dance: 
Dragonite
Quiver Dance: 
Volcarona
Iron Defense + Body Press: 
Corviknight

Garganacl
Attacking move: 
Skeledirge (Torch Song, and sometimes Flame Charge)
Likely to be viable
Bulk Up: 
Slither Wing

Quaquaval

Corviknight
Curse: 
Garganacl

Clodsire
Dragon Dance: 
Roaring Moon
Calm Mind: 
Sylveon

Stored Power Espathra
Iron Defense + Body Press: 
Iron Treads

Iron Hands
Likely to be niche
Bulk Up: 
Ceruledge

Scream Tail
Curse:
Tyranitar
Calm Mind:
Blissey

Scream Tail

Gothitelle
Iron Defense + Body Press: 
Orthworm