Been meaning to post here for a minute. I have always liked SS DOU and thought it was probably the most overhated gen. It doesn't really have glaring mechanical flaws - terrains are nerfed from SM, crits are 1/24 @ 1.5x, tapu fini exists, etc. Dynamic speed is the one that gets brought up a lot but I think the tailwind clickers in SS are strong but not overtuned like SV Tornadus.
Out of the 4 official DOU tiers in the oldgen circuit I only joined SS and XY cup, my favorite of the two. I spent most of Swiss recycling the double Meteor Beam Tailwind I made with Animus for SCL 2 (you can see some highlights of that in the post above) and a Cosmic Power Metagross + NP Grassy Seed Spectrier team I made at some point.
For top 16 vs ratpacker I built this team and used it in every set I played afterwards (click sprites for paste)
Title says it all, I wanted to see if backporting Tornadus + Urshifu into SS DOU from SV VGC felt good. I chose CB Urshifu to accomplish this because it allowed me to invest in bulk considerably. I really like Life Orb Tornadus but I felt like adding Politoed to the team would end up making it too similar to existing rain teams which a lot of people already build/practice against. So I made the Tornadus run Rain Dance. Unfortunately in gameplay I didn't always have the time to click Rain Dance before going for Hurricane, but hey it's still more accurate than hitting both targets with Bleakwind Storm...
To use a Choice Band Urshifu in SS, you're absolutely going to need some form of priority block. Between Tsareena and Psychic Terrain, I chose the latter as I figured an Urshifu centric team would be good at clearing common Psychic resists. I opted for a WP Necrozma with Heat Wave retroactively after deciding I wanted to run Scarf Naganadel, which was a decision made to get the jump on Dragapult, Scarf Tapu Fini, and the occasionally-still-relevant Scarf Genesect. I preferred it to the Meteor Beam set because I really wanted Fire coverage on this Necrozma and didn't want my only move to hit Incinineroar be a move that I could whiff once and be screwed for the rest of the game. Eject Button Amoonguss rounds out the team to bring it some stability and pressure semiroom as Lele + Amoonguss is typically pretty annoying for these guys.
I generally like these tailwind HO structures in SS a lot. If you're fed up with triple Fake Out teams and looking for something else to try I'd say try out this, the Nihi Steela team, or Dracovish Torn Rain. I hope people will keep building in this tier and pushing it further, I think the potential for this tier to be a well respected oldgen is absolutely there.
Put vish in tier 2 he deserves it.
Out of the 4 official DOU tiers in the oldgen circuit I only joined SS and XY cup, my favorite of the two. I spent most of Swiss recycling the double Meteor Beam Tailwind I made with Animus for SCL 2 (you can see some highlights of that in the post above) and a Cosmic Power Metagross + NP Grassy Seed Spectrier team I made at some point.
For top 16 vs ratpacker I built this team and used it in every set I played afterwards (click sprites for paste)
Title says it all, I wanted to see if backporting Tornadus + Urshifu into SS DOU from SV VGC felt good. I chose CB Urshifu to accomplish this because it allowed me to invest in bulk considerably. I really like Life Orb Tornadus but I felt like adding Politoed to the team would end up making it too similar to existing rain teams which a lot of people already build/practice against. So I made the Tornadus run Rain Dance. Unfortunately in gameplay I didn't always have the time to click Rain Dance before going for Hurricane, but hey it's still more accurate than hitting both targets with Bleakwind Storm...
To use a Choice Band Urshifu in SS, you're absolutely going to need some form of priority block. Between Tsareena and Psychic Terrain, I chose the latter as I figured an Urshifu centric team would be good at clearing common Psychic resists. I opted for a WP Necrozma with Heat Wave retroactively after deciding I wanted to run Scarf Naganadel, which was a decision made to get the jump on Dragapult, Scarf Tapu Fini, and the occasionally-still-relevant Scarf Genesect. I preferred it to the Meteor Beam set because I really wanted Fire coverage on this Necrozma and didn't want my only move to hit Incinineroar be a move that I could whiff once and be screwed for the rest of the game. Eject Button Amoonguss rounds out the team to bring it some stability and pressure semiroom as Lele + Amoonguss is typically pretty annoying for these guys.
I generally like these tailwind HO structures in SS a lot. If you're fed up with triple Fake Out teams and looking for something else to try I'd say try out this, the Nihi Steela team, or Dracovish Torn Rain. I hope people will keep building in this tier and pushing it further, I think the potential for this tier to be a well respected oldgen is absolutely there.
Put vish in tier 2 he deserves it.
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Won't write much about these because they add so much value to the board its insane. They even compliment each other, as Rillaboom can provide extra sustain for Fini and Fini can block status moves like WoW for Rilla. Very dumb mons that can run a plethora of items and do amazing anyway. You can't go wrong adding these two to your team. 
: WOW I'm surprised so many people hate on this thing and rank it T2 or even lower. I think this is an amazing Pokémon, provides so much to every single existing archetype (except like hard weathers) and has the only drawback of being Taunt food (and even then the coverage moves you can run help a lot). You can put Hazards on this thing, status, speed control (in tailwind AND trick room!), fake out, coverage like Flamethrower, Ice Beam, Earth Power, it can be your win condition with Cosmic Power & WP, can even be an annoying utility with Snarl, Encore, hell this thing is amazing. When SS was current gen I was even thinking this deserved a suspect test. Not anymore because Fini & Rilla are kinda better now but yeah, this thing is just goated. 
: Ok, this mon is actually very good. When you use the good sets. Can you people PLEASE stop using Assault Vest? Sure you tank so many hits and you are able to pivot out of many situations, but man Shifu doesn't want to be a pivot, it wants to nuke shit. AV is only good when your opponent gifts 3 turns for you to Coach it. I gave it a chance in one of my games and never again, thing SUCKS. I agree with zee's above post though, Shifu might want some sort of bulk, but damn not 252 hp 252+ spd AV.
: Another Pokémon I'm surprised it has been rated so low. Only real set is 252 HP one, offensive is whack, but this thing provides again so much utility while having a very solid STAB to hit the popular water type Pokémon on the tier. It can also Knock Off items, spam Coaching, Taunt stuff, and let's not forget Fake Out. U can even run "weird" moves for this tier like Snarl, Blaze Kick, and even funny moves like Fling to self-proc Weakness Policy + Berry. Even in games where it faces Zygarde + Double Grass it has some sort of utility. I can see it being Tier 3, but imo has enough to barely be a T2. 
: 80 + 80 = 1600. The pressure this thing creates is MASSIVE. Probably the Pokémon that punishes the most when you play it aggresively and barely leaves a chance for opponent to come back once it picked 2-3 good turns. You can run it anywhere, and however you like it. It can be Band on Tailwind Rain teams, it can be scarf on speed control-less teams, it can be Band on Sand Tailwind teams, it can even be a funny item like Safety Googles, Mystic Water, etc etc with Sub Protect. Same case as Zeraora, I can see this on Tier 3 as well since it's very easy to run a Prio Spam team or redirection Pokémon like Amoonguss or Indeedee and it will lose a lot of momentum, but yeah you can't deny the pressure it creates. 
: I only noticed it on finals, but there are a lot of teams that suffer to this thing. And do you know what the best set is? CHOICE BAND. You can nuke 252 HP Zeraora with Close Combat, has a good chance to KO 252 HP Mew with U-Turn, its so funny! But yeah I guess boring LO and Sash are also usable sets. Anyway this thing is like Dracovish but harder to enable and easier to kill. Still, I think it's a very good pick, and I hope to see it more on future tournaments!
This thing was pretty bad when SS was a current gen, but somehow is now very good? It's an amazing fit for HO teams, packs disrupting moves such as Taunt and Encore, and is able to help your teammate with Fake Tears (if its special attacker only). Ngl I forgot this existed and loaded some teams with no speed control and almost costed me the game lmao but yeah it is actually very good and you should consider it on your builder!
Weather 
: I think most weathers are fine. Imo, its rain > sun > sand >>>>> hail, but yeah basically all of them are usable. Rain abusing Pokémon deal massive damage even to their ressists, and virtually OHKO anything that is neutral. Kingdra is in a rough spot though, it has a super weak Muddy Water and it's always bad when you rather click the Draco button or Hurricane button instead of funny spread damage one. Sun is great imo and should be on the rise. When I started SSPL I saw so many Double Water teams having success at DPL, so I went and brought Venusaur team back. I didn't face what I was expecting to face when I loaded it, but it still did a good ammount of work. Sand can be disrupting to a lot of teams because you can enable the two broken fossils, and sand cheap is great to pick up KOs you previously weren't picking up (An example being Mew for Dracovish if you aren't band). Hail... well, its a funny weather, you'll have fun if you load it :D!
Trick Room 
: Ngl I think Gen 8 Trick Room is probably the strongest Trick Room we have on Fairy Gens. A lot of Pokémon that like to be on Trick Room deal massive damage to a lot of "standard" structures. Thing is you have to perfectly use your turns on Trick Room or you will stay behind even if you have the speed control, and the most important thing that is often overlooked, is how is your position when Trick Room ends. A lot of games are actually decided on this turn!
(The DD one) Set-Up 
Is Dracovish Too Good? 
4 -> 3
5 -> UR