In light of the Land-I ban (props to the council for this), I wanted to share this set I came up with:

Landorus-Therian (M) @ Leftovers
Ability: Intimidate
EVs: 252 HP / 4 Def / 252 SpD
Careful Nature
- Earthquake
- Protect
- Toxic
- Knock Off
With Land-I no longer able to use HP Ice, SpDef Gliscor would be a near-perfect counter. However, Gliscor is of course not available, so I decided to imitate it with Land-T. I tested this on ladder (my alt was ltpd 30 rock) and it was excellent, reliably handling Land-I every time I faced one. While it doesn't have Gliscor's amazing recovery combination of Poison Heal + Roost, it is actually bulkier than Glisc (382 HP + 284 SpDef vs. Gliscor's 354/273), and Protect + Lefties gives it solid longevity. Between Toxic's crippling effect complemented by Protect as well as Knock Off removing Life Orb and accelerating the effect of the poison, this set could even handle Gravity and CM Land-I variants fairly well.
The SpDef wasn't just good for Land-I, though - it didn't hard counter much, although one of the few pokes it did hard counter was Specs Koko, which was excellent. Having a long-term Electric immunity was also great for Regieleki. However, what this set did do was give me the flexibility to play around a LOT of major threats with greater ease: most notably, things like Spectrier (Specs Shadow Ball almost never 2HKOs from full and never will with Protect), Torn-T (unboosted Hurricane isn't a guaranteed 3HKO, +2 Hurricane doesn't come close to KOing), and Latios (Specs Draco doesn't come close to KOing, means I don't necessarily have to scout with Protect/switch after using Protect and can instead be more aggressive). Obviously, I preferred to primarily check these Pokemon with my other team members, but having different options was really nice against teams with lots of dangerous threats - if I had a situation such as, say, my Hydreigon struggling to fend off Heatran + Spectrier, then Land-T stepped in and did an admirable job backing it up. Torn also tended to use Land-T to set up Nasty Plot, which was amusing: it'd eat a Toxic, then I'd Protect, then Knock Off, then Protect again...
The bulk was nice in some more extreme situations, too - Land-T (can't wait to just start calling it "Lando" again as soon as we get used to Incarnate no longer being around)) is overwhelmingly favored (87.5%) to survive offensive Magearna's Ice Beam, and 4 SpAtk Pheromosa tops out around 88%.
I think don't think the SpDef is really that needed anymore now that Land-I is no longer around - Defense will probably be more useful for handling things like Blaziken, Cinderace, Excadrill, Melmetal, Rillaboom, Kartana and Tapu Bulu. However, that is almost secondary because this Lando isn't just a wall - its moveset makes it an offensive weapon. With Gliscor, Megas and Z-Crystals not around, nothing takes Knock Off safely, and Toxic + EQ cripple the better Knock "absorbers" in Regenerator Slowbro / Tangrowth / Toxapex. Even the Tox-immune Amoong doesn't like EQ, especially with rocks up. Also, these Pokes losing their Boots means this set is excellent alongside Ferrothorn's Spikes.
As a whole, Land-T can threaten just about the entire tier with this set. The closest thing that comes close to being able withstand that trio of moves is ResTalk Zygarde, which I faced on one stall team (and still gets Knocked, and Zyg as a whole will hopefully be banned soon as well...), and Corviknight, since it can Roost. Even then, a Knocked Corviknight is super exploitable, whether with pressure from offensive teammates (such as Melmetal, who now comes in and threatens it freely), or with Magnezone capitalizing on the lack of Shed Shell. Plus, Land-T's EQ is strong even without investment, letting it chunk things like a Knocked Clefable. It doesn't need to run 0 Attack, though - without the need for SpDef, I could easily see it running some investment, as an Adamant nature with 0 EVs is nigh-guaranteed (99.6%) to 2HKO Kartana, hits Clef even harder and leaves plenty of room for HP/Defense/SpDef/Speed EVs.
To support this claim, I used the team I made with this Land-T in several Smogon Tour games, and didn't face Land-I with it once, but the moveset repeatedly put in work:
https://replay.pokemonshowdown.com/smogtours-gen8ou-524735 - harassing screens offense by coming in freely on Koko and Regieleki, all it had to do was not use Toxic until Mew blew up so it wouldn't get Synchronized, and from there it was insanely annoying to KO. Toxicing Hawlucha is a big deal, when I played teams like that on ladder it crucially allowed me to do things like save my Clefable for Zygarde. Even teams with more threats than this one (like Kyu-B, Pheromosa and the aforementioned Zyg) will struggle to switch into Land-T. The SpDef didn't really make a difference here, as I was ready to revenge the Magearna with Scarf Spectrier, but it got to show off how tanky it is by soaking up that Stored Power.
https://replay.pokemonshowdown.com/smogtours-gen8ou-524821 - hella long game, and I could've made more effective use of the Land-T as well as Melmetal, but this is an example of how irritating it can be against even super defensive teams.
https://replay.pokemonshowdown.com/smogtours-gen8ou-524858 - Toxic/Knock threatens everything. Intimidate + Lefties Protect gives Clef some security against CB Zyg (keeping it away from Iron Tail and allowing Clef to maintain Softboiled PP + stay healthy for Buzzwole).
https://replay.pokemonshowdown.com/smogtours-gen8ou-524863 - cripples Corviknight, allowing Melmetal to go berserk, and helps play around Smooth Rock-supported Exca. Checking the rogue Dracozolt is nice too (while calcing, I was amazed to learn that CB Hustle Bolt Beak OHKOs Melmetal).
I would've loved to have included Wish on Clef, but couldn't fit it alongside the other Pokes I wanted to run - however, on another team it'd have been a match made in heaven, as would've been a Spikes Ferrothorn. Those replays also showcase something else I wanted to mention briefly: Melmetal is an absolute
monster, especially with Protect. In addition to countering Kyu-B, it was also an amazing check to BoltBeam Magearna. Double Iron Bash outdamages supereffective EQ and threatens to KO offensive Gear after Stealth Rock, while SpDef investment means even boosted Thunderbolts bounce off...what a beast.
That's about everything. Can't wait for KyuB/Zyg to go next. Thanks for reading!