Idk smogon has had odd policy regarding forme changes in the past as well. One of the easiest examples is Genesect, which technically has 5 different forms that could hold different drives, but we're banned mostly for - from the outside looking in - vibes-based reasoning like "Shift Gear is still broken", "its too similar to the base form", "Douse Drive let's it beat its counters" (which in that case ban Douse Drive and let it use the other drives). Maybe this is all true but it never got any due process to my knowledge.
I do agree a broader definition of forms would be nice - because as far as I'm concerned - genesect with drives is no different than something like Zamazenta-Crowmed or Ogerpon forms in the sense that it has a different page in the pokedex, it is Item locked (so can't be tricked or Knocked off), and it affects a specific move it runs.
With Terapagos - the arguenent against unbanning it at least makes sense since you are preventing a core mechanic of the game from being used. It would be like banning switching so that a player could use just Baby palafin instead of Palafin Hero. Obviously not 1-1 and Terapagos at least has some precedent given how Mega Rayquaza was handled + i am more biased in including Terap in the tier through some means lol, but I do see the arg for banning it is what I'm trying to say
Magcargo made a very interesting point about Genesect and why the argument against unbanning Terapagos-Terastal makes sense. As he'd indicated, Genesect when holding any of its Drive items cannot have the item-removal effect from Knock Off triggered, doesn't take the 1.5x damage from Knock Off, cannot be affected by Trick and Switcheroo, and Techno Blast's attacking-Type changing depending on the specific Drive item used is quite notable.
Even if Genesect with its different Drive items don't have different Pokédex entries, there is already a precedent on this with the alternate forms of Rotom, which don't have their own separate Dex entries and personally, I'd say Genesect holding one of its Drive items shares more in common with mons such as the alternate Ogerpon mask forms given it not being able to lose its item, how it cannot be affected by Trick or Switcheroo while having a specific signature move, Techno Blast, that changes type much like Ivy Cudgel does even if it doesn't have a typing change like the alternative Rotom forms do. I believe the case can very much be made that Genesect holding a Drive item is functionally a different Pokémon than base Genesect given its differences and limitations compared to the base form, standing out more than the alternate Rotom forms due to its item limitation, Knock Off, Trick, and Switcheroo immunity, and changing Technoblast type compared to the alternate Ogerpon forms even if it doesn't have a changed typing or a moveset changed compared to the alternate Rotom forms, which don't even get a signature move of their own but a widely available move that corresponds to their respective alternative typings.
However, I don't see the justification for unbanning Terapagos-Terastal 'cause Terapagos-Stellar's transformation is directly tied to the Terastal mechanic, and one wouldn't play every match or even nearly every match determined to Terastalize Terapagos-Terastal no matter what if the opposing team has a very solid check or counter to it. The only even remotely similar comparison would be the case of Slowbro and Mega Slowbro if the opposing team has loads of hazards, you have poor removal or your removal matches up poorly against the opposing team, and the opposing team doesn't have a physical beast that requires one to use Mega Slowbro to check, but in most cases, one will want to use Mega Slowbro eventually during the course of a battle, not to mention that just holding Slowbronite limits the amount of choices available to Slowbro even in its base form since it can't hold another item, cannot lose its Mega Stone, and takes decreased damage from Knock Off.
Banning Terapagos-Terastal from Terastalizing is very much arbitrary and has no predecence in OU. Yeah, I know, there's Mega Rayquaza, but that's an Uber-specific precedent from a format that priorititizes banning as little as possible, and you'd choose to Mega Evolve to Mega Rayquaza every time given how much of an upgrade compared to Rayquaza it is. Terapagos-Terastal also can very much have its item removed, and you wouldn't use your Tera on it every time given how important Tera is as a mechanic even if Terapagos-Stellar is extremely powerful for OU, and much of its effectiveness is also innately tied to Terapagos-Terastal's Ability, Tera Shell, that in conjunction with Heavy-Duty Boots, gives it more leeway to be a centralizing force. While I agree that Terapagos-Terastal would be a healthy addition to OU, I believe making it available breaks too much precedents in OU by denying JUST ONE Pokémon the ability to use a universal mechanic, especially since you'd have to clause it for it to be legal in OU.
As for what tiering action I would like to see, it'd only be Ceruledge or Light Clay due to just how rewarding players properly positioning themselves to give Ceruledge an opening is one reason why Screens HO is as powerful as it is as an archetype, in part due to how much role compression Ceruledge provides as well as how much of an immediate threat it is despite it not being used on every Screens HO 'cause of how much of an immediate threat it is given how strong its STAB combo is with Poltergeist being nuclear and how Bitter Blade is a cheap move that lets it duel 1v1 and heal itself against mons it shouldn't have any business doing given Bitter Blade is already a 90 Base Power move and didn't need such a powerful effect given Fire is already a top offensive typing.
Ideally, I'd prefer action on Ceruledge first since I believe a ban on Ceruledge would be enough to rein in Screens HO due to the mere threat of Ceruledge on Screens HO and also outside of it due to how punishing misplaying against it is. If Screens HO is still nearly as consistent and strong as it is after Ceruledge is gone, I guess a Light Clay suspect could make sense given even after a significant teambuilding pressure had been removed, Screens HO still being borderline an issue would be a problem. Although I could be wrong on Cresselia, I feel the meta is moreso going through a phase similar to when some people struggled against Pecharunt heavily due to people starting to use it to its full potential. Although Cress is very strong now, I don't think it's outright broken, at least not yet, and I believe there shouldn't be any immediate action on Cresselia, and I personally find it useful as a defensive glue and as a win con in a tier littered with threats that has reasonable counterplay in Encore, Taunt, and physical set-up. That isn't to say I don't understand why some people want Cress suspected as I do believe Cress is a better mon than Garganacl ever was and Garg was never broken as players started learning how to play against Garg.
Roaring Moon just has no chance of being unbanned if given a suspect test given Volcarona was a less contentious Pokemon and was banned by a comfortable margin despite Volc being way more reliant on Tera Blast than Roaring Moon ever, not to mention Roaring Moon also being a much more immediate threat through its much better coverage options compared to Volcarona and its higher speed, meaning there'd likely be more support for keeping Roaring Moon banned than Volcarona. Roaring Moon, even if it were to drop to limit scarf Gholdengo, Samurott-Hisui, Ceruledge, and Ogerpon-Wellspring usage would just make HO stronger, which isn't something needed right now. Roaring Moon was also a big threat even without Tera Blast Fairy, so I fully believe suspecting it would be a waste of time since all it'd do is make the meta worse before the end of the generation when actions should be taken to improve the meta rather than make it worse.
As for re-suspecting Tera Blast, I don't think that is necessary or even wanted by much of the playerbase. Allowing a Pokemon to randomly cheese counterplay with a coverage option it normally wouldn't have access to isn't fully healthy since type advantages, at least before Gen 9 was introduced, were core to the fundamentals of the game. There's a reason why some people didn't enjoy shit like Z-Giga Impact Kartana in Gen 7 'cause let's be real, nobody would regularly use Giga Impact Kartana if Z-Moves didn't exist as the downside of Giga Impact was so huge, and Tera Blast giving one access to strong coverage that can be STAB-boosted with the only drawback being committing your Tera to that Pokemon with Tera Blast in its moveset isn't as much of an opportunity cost as some people propose it to be. Based on your opponent team's composition, one will have a good idea whether your Tera Blast mon is what you need to advance the game state and one's positioning toward a win, so it's overblown how much of a sunk cost having a Tera Blast sweeper is.
So my preferred order of action would be:
1. Suspect Ceruledge
2. Suspect Light Clay
3. Do Nothing
