Hey thanks
The Ruins of Alpha for spotlighting Bad STABmons! I really enjoy this format and I'll share my feelings on viability below.
Overall, Bad STABmons is much kinder to other playstyles. Stall, semi-stall, and bulky offense are way better here, while hyper offense is nerfed to an extent because there are some really potent defensive cores that can be difficult to break if you don't prepare.
I'll just kinda list what I think are top offensive & defensive threats with some arbitrary pseudo rank attached to them.
In order of BST:
Offense
One of my favorite Pokemon in this format, Doublade sports a fantastic typing and a behemoth Defense with Eviolite and as such it's one of the best FakeSpeed checks, but it's primarily used as an offensive threat. With the No Guard ability, Doublade has a perfectly accurate STAB Iron Tail with a cool 30% chance to drop the target's Defense, which puts pressure on walls. It also usually carries Sacred Sword and Shadow Sneak and the last slot can be Swords Dance, Pursuit, Gear Grind, Bullet Punch, King's Shield, or Shadow Claw.
==Probable Rank==> A
Kecleon sports a solid base 90 Attack and access to a lot of priority, which mitigates that awful Speed. Generally it's used as a FakeSpeeder but what sets it apart from things like Rufflet and Raticate is its access to STAB Knock Off to punish Doublade, STAB Fire Punch to hit Ferroseed, and STAB Ice Punch to savage Gligar. While it can't run them all with FakeSpeed, it can cater its set based on your team needs quite well, making it extremely versatile.
==Probable Rank==> A/A+
Rotom is one of the faster attackers in the metagame, tying with threats such as Murkrow and Chatot, the latter of which it checks well, or outspeeding everything with a Scarf attached, which allows it to revenge the plethora of birds in the tier. Most notably it provides a fast answer to Rufflet and unlike Doublade can keep up the momentum for your team quite well. Besides running Scarf it does double status + Hex well.
==Probable Rank==> B+/A-
Sneasel is basically doing what Weavile does in regular STABmons with a notable buff in Speed, as it's the third fastest Pokemon after Swellow and Dugtrio (and ties with Persian but no one besides
wishes uses that). Any combination of Knock Off, Icicle Crash, Ice Shard, Pursuit, Parting Shot, Swords Dance, and Low Kick work. Use it to revenge birds and Rotom and to scare off Doublade and Gligar.
==Probable Rank==> A-
One of the best wallbreakers in the format, Hustle Zweilous hits really, really hard. Usually carrying a Choice Band or running Eviolite to ease setup with Dragon Dance, it's truly a threat to watch out for, as not much in the metagame can stomach its Dark / Dragon STAB and Superpower. It doesn't even need a move for Fairies because most of the time the raw power of its attacks allows it to muscle past them regardless. It's held back by a bad base 58 Speed, but with +1 under its belt, it can actually outspeed a fair amount of Pokemon.
==Probable Rank==> B+
Bad STABmon's "Ursaring", if only because of Guts. The nice thing about this FakeSpeeder is its access to U-turn to pivot out of Gligar, Doublade, and Ferroseed. It hits a tad bit weaker than Guts Swellow but it isn't held back by a crippling Stealth Rock weakness, which for FakeSpeeders, is a real pain.
==Probable Rank==> B+
Servine is identical to its evolved counterpart in every way with the exception of a worse Speed tier. Still, 83 is usable. Like Serperior, Servine spams Contrary Leaf Storm and uses Spore to disable its checks and counters. It doesn't have Dragon Pulse, but it doesn't really need it. The choice between Hidden Power usually falls down to Fire for Ferrothorn or Rock for Togetic and Fletchinder. It's fairly one-dimensional but don't underestimate it in the slightest.
==Probable Rank==> A
Chatot is one of the few viable Boomburst spammers in the format, which is a nice change of pace for players annoyed by the prevalence of Sylveon in regular STABmons. In Bad STABmons, Chatot acts like a pseudo Thundurus with a set of Taunt, Nasty Plot, Boomburst, and Oblivion Wing. There's also Heat Wave for coverage but that's really only needed for Doublade and a +2 Oblivion Wing is still going to do a large chunk. Substitute sets can work without Boomburst or a Choiced set with Hurricane in there somewhere.
Remember: Chatter is banned, even on Chatot.
==Probable Rank==> A-
Don't laugh but Pupitar is a potent threat if you underestimate its potential. While its defensive merits look appealing, what makes it scary is access to Dragon Dance, Rest, Diamond Storm, and Precipice Blades and the ability Shed Skin while holding an Eviolite. Rock typing ensures it can't be revenged by FakeSpeed easily if at all. It also makes a nice offensive hazard stacker. With Rest it's probably the best Fletchinder counter out there.
==Probable Rank==> B/B+
RoA already mentioned how dangerous Bibarel is but it bears repeating. If the opponent doesn't have a Ferroseed, Quagsire, Shedinja, or Doublade or their own faster FakeSpeeder, it might as well be GG. Bibarel can run a 4th move to beat all those checks, however: Superpower, Grass Judgment, Pluck, Ghost/Ground Judgment, and Protect. Besides Swords Dance it also can run Curse, Growth, and Acupressure, making it hard to prepare for.
==Probable Rank==> BANNED
Combusken may be short on variety but what it does it does superbly well. A set of Protect / Swords Dance / V-create / High Jump Kick or Drain Punch threatens nearly every wall, leaving only Quagsire, Gligar, and Thick Fat Azumarill able to switch in safely. There's some wiggle room with things like Substitute, Baton Pass, and a less detrimental Fire STAB if necessary.
==Probable Rank==> A+/S
Dugtrio is the second fastest Pokemon and it's able to trap and eliminate a ton of threats for your team. It's very frail and prone to being revenged, but if it's able to remove an Audino or a weakened Quagsire, it's done its job. It can also throw out Spikes in between kills or from behind a sub, making it a good stacker too.
==Probable Rank==> A-/A
Don't let its low BST fool you: Frogadier is a top-metagame threat. It boasts a nice 97 Speed, allowing it to revenge kill a lot of the metagame quite comfortably. Access to moves such as Steam Eruption, Ice Beam, Dark Pulse, Hidden Power Fire, and Grass Knot puts a ton of pressure on opposing teams. Plus it has utility moves such as Toxic Spikes and U-turn to abuse switches. It's really good but it can be held back by a lack of power, as 83 Special Attack isn't always enough to muscle past fatmons like Audino and Togetic.
==Probable Rank==> A+
Bad STABmons' other Thundurus, Murkrow can use its Taunt + Nasty Plot set to shut down stall teams with ease and plow through them with Oblivion Wing and Dark Pulse or Night Daze. And in true Thundurus fashion, Murkrow also has the potential to be wholly physical too with Dragon Ascent and Knock Off. Prankster is typically preferred so it can Parting Shot and Taunt with priority, but Insomnia is a viable option to check Servine.
==Probable Rank==> B+/A-
While Togetic excels at playing support roles, it's also a huge offensive threat you have to watch out for. It has two very good abilities in Serene Grace and Super Luck and access to Nasty Plot, Oblivion Wing / Air Slash, and Moonblast plus Fire Blast for coverage. Thanks to the Eviolite item, it's absurdly bulky and can use that bulk to set up on most of the metagame with ease. It can even tank most FakeSpeed attempts and retaliate with a powerful move of its own.
==Probable Rank==> S
The format's best Belly Drummer, Munchlax is very similar to Snorlax but here it's even bulkier and harder to crack. Besides the common BellySpeed combo, Munchlax can also set up with Curse + Normal recovery move of choice or just use Swords Dance. Fire Punch is helpful to eliminate Ferroseed and Earthquake hits Doublade hard. As a standard FakeSpeeder it can run Pursuit to catch fleeing foes.
==Probable Rank==> A-
Another low BST, high viability Pokemon, Fletchinder is a standard on most teams and for good reason! STAB Dragon Ascent allows it to revenge kill a lot of the frail offensive threats in the metagame and unlike some other birds it has a SE STAB to punish Doublade with. Sacred Fire makes for a solid secondary attack, but some even go full-blown V-create for wallbreaking. Swords Dance turns it into a formidable sweeper and Taunt with or without Will-O-Wisp helps it break down walls such as Quagsire and Gligar that try to check it.
==Probable Rank==> A+
It's not a common sight but Cranidos is a real terror that can take a lot of people off guard, especially when its equipped with a Choice Scarf. Diamond Storm gets the boost from Sheer Force, making it slightly weaker than Head Smash but without that nasty recoil and with better accuracy. Fire Punch, Earthquake, and Pursuit or even Ice Beam are options to round out its arsenal. But really, it just spams Diamond Storm.
==Probable Rank==> B+
Hustlet is the most unreliable revenge killer in Bad STABmons but it's also the strongest by far. When it does hit, things die. FakeSpeed is its bread and butter, plus it's got Dragon Ascent, Superpower, and Shadow Claw to round out coverage. If it's not running FakeSpeed, it probably has a Choice Band, which does the same as FakeSpeed but all in one turn instead of two, thus limiting Leftovers recovery and ignoring Protect's attempt to burn Fake Out.
==Probable Rank==> A
Defense
Liepard isn't a wall by any means, but it's a valuable utility Pokemon thanks to Prankster Parting Shot, Taunt, and Thunder Wave. And while Murkrow can do these things too and has solid recovery, Liepard doesn't take as much Stealth Rock damage, hits a bit harder, and doesn't rely on its item nearly as much. It has a good mixture of offense and utility, but it's the utility that most people use it for.
==Probable Rank==> A-
Bad STABmon's pink blob. Audino is really good here with its unrivaled natural bulk on both defenses and the ability Regenerator, which allows it to pass Wishes or utilize Baton Pass extremely well. (Think of Stockpile or Swords Dance stuff.) It can't do much back but at least Boomburst has a high base power. Other utility options include Glare, Heal Bell, Toxic, Rapid Spin, and Knock Off.
==Probable Rank==> A/A+
Quagsire alone invalidates so many physical threats that it should always be considered when building a well-rounded Bad STABmons team. You'll often see it with a status move like Toxic or Scald (or both), Recover, Ground coverage, and then maybe Spikes, Protect, or even Curse. It's boring. It's predictable. But you
have to plan for it somehow or you won't get anywhere in this format.
==Probable Rank==> A+/S
Gligar is a lot like Landorus-T here and often runs hazard support sets with either Defog or Stealth Rock / Spikes. Roost ensures it can stick around to wall physical attackers throughout the match and U-turn helps it keep up the momentum. Flying STAB is rare but Earthquake or even Precipice Blades give it an offensive bite when needed. Immunity keeps it free of Poison, but Toxic isn't too common except on other walls, which it can't really beat.
==Probable Rank==> A-/A
As Huge Power is banned, Azumarill must run either Sap Sipper or Thick Fat, and both abilities are good for this format. Sap Sipper lets it wall all variants of Servine and Ferroseed while spinning any hazards. With Thick Fat it can stomach Combusken's onslaught and tank all of Sneasel's attacks with ease. Water / Fairy / Normal moves grants it access to a list of goodies such as the aforementioned Rapid Spin plus Recover, Heal Bell, Glare, Baton Pass, Scald, and other standbys like Knock Off.
==Probable Rank==> B/B+
Sure, it can be a special sweeper, but it's unmatched when it comes to defensive support due to its amazing defensive typing and huge bulk with Eviolite. Defog, Roost, Moonblast, and a filler move such as Oblivion Wing or Thunder Wave is a pretty standard set. It pairs excellently with Quagsire, taking any Grass moves directed toward Quagsire and sending Rock, Electric, Poison, and Steel back. TogeSire can be quite hard to crack and forms probably the best defensive core in all of Bad STABmons.
==Probable Rank==> S
Porygon is another pre-evo that functions quite similarly to its evolved form. Like Porygon2, Porygon can abuse Download + Baton Pass well and even take advantage of the boosts for itself with Boomburst and Extreme Speed. It will have Recover to stay around longer and sometimes Glare to slow things down to a more manageable speed.
==Probable Rank==> B+/A-
With its Steel typing, Mawile makes an excellent Bird check, and now has Moonlight to regain health throughout the match. Stealth Rock is pretty common on any Mawile set to keep those pesky birds at bay even more and if needed it can attack with moves such as Play Rough and Gear Grind.
==Probable Rank==> B+
There are other good Grass Pokemon capable of playing supportive roles such as Tangela, Foongus, and Pumpkaboo, but with Ferroseed around, there's really no point in using them because Ferroseed offers so much utility in one Pokemon. It has access to two hazards plus Leech Seed to dissuade switch-ins. King's Shield or Spiky Shield help it water down foes or ramp up the chip damage, respectively. When it comes to attacking Ferroseed is weak, but Gyro Ball can be used to punish faster foes such as Servine, which otherwise has little to fear from Ferroseed.
==Probable Rank==> A
Shedinja can be dead weight if not played correctly, but with the right support it can shut down a ton of threats all by itself. Unfortunately most of the offensive threats listed above have moves that hit through Wonder Guard so in some matches it's relegated to just checking FakeSpeed. It makes a nice hazard stacker with Sticky Web and Spikes and can spread burns and pivot out of trouble with Baton Pass.
==Probable Rank==> B-/B
There are lots of other viable threats, both offensive and defensive, that aren't covered above. Some include Tinted Lens Noctowl, Swellow, Simple Swoobat, Magcargo, Sheer Force Croconaw, Mantyke, Corsola, Clamperl, Yanma, Lickitung, Krokorok, and Pawniard (and more!). This format is still really unexplored, so if you ever want to try it out, join the Neon Town room on Pokemon Showdown!