I initially had an entire rant typed out about Terastallization and why it's problematic, but instead I'd like to talk about the various alternatives to an outright ban. While I still do believe our best option to be an outright ban that we will eventually get to, one of these suggestions would be fine to try out and see how they work, while the others are pretty bad.
To start, I do not believe we should alter the mechanic so intensely and widely to preserve it. What I mean is that if you have to have 3+ clauses to make Tera legal, it really feels like we're jumping through hoops and avoiding the fact that the broken mechanic needs such massive nerfing to work and we should probably just get rid of it. I also believe we should keep the fundamental aspects of Terastallizing, or in other words, I disagree with locking it to same type tera OR banning same type tera.
The latter doesn't even make sense, it's why Terastallization is so busted, as so many threats like Kingambit, Volcarona, Annihilape, Gholdengo, Roaring Moon, Gargancl, Dragonite, etc all change to a different type and become extremely good with their newer defensive utility vs counterplay. Sending my Breloom to revenge kill Roaring Moon only to see "oh great, tera flying, guess I lose" is a problem. Locking to same type Tera still creates the issues of giving free Adaptability to many Pokemon but it is easier to handle than locking to non STAB. However, some stuff will still be broken though like Dragapult. Regardless, I still oppose it because then we are taking away the point of Tera, which is the ability to become any type lol. We would just end up making our own mechanic and deviating from the very core of it. I get we’re taking a more complicated route but these options are too extreme from the purpose of Terastallization. Hard no on these solutions.
Furthermore, banning Tera Blast is largely a mistake as well, because the most significant Tera benefactors rarely if at all run Tera Blast. Let’s take a look at them below, it’s a combination of the list made by Finchinator
plus others I’ve run into in my own experiences. I also figured it would be useful to have the most infamous users in one place and there's probably more I forgot.
-The most prolific Tera abuser and honestly the prime example of balanced Pokemon broken by Terastallization, it would not nearly be as difficult to deal with without Terastallization. Roaring Moon often runs Tera flying with Booster Energy to give a powerful STAB Acrobatics since its item is consumed while evading Mach Punch from Breloom. Tera steel is also used to put extra power behind Iron Head for Fairy-types and avoid being revenge killed from attacks like Ice Shard from Chien Pao, Moonblast from Iron Valiant, Draco Meteor/Dragon Darts from Dragapult, and Bullet Punch from Scizor. Tera dark is another set used to put extra power behind Dark STAB. Does not run tera blast.
-Dragapult typically runs Tera Ghost to either give it essentially Adaptability Shadow Ball or a reliable physical Ghost-type STAB in Tera Blast, making it often very difficult to beat defensively. Sometimes runs Tera Blast but also has sets where it does not.
-runs Tera Normal 95% of the time but Steel and Fire have uses for beating Fairies and avoiding Ice Shard while the latter also lets it break through Corviknight easier. Generally though, Multiscale giving Dragonite immense setup chances coupled with a solid Normal typing and extremely powerful Extreme Speed make it a top 3 tera abuser and it's honestly broken. However, this does not run tera Blast.
-runs Tera fighting or Tera water, the former gives it a powerful boost to Body Press while the latter is just a strong defensive typing that can make Gargancl unkillable at times. A Pokemon balanced by its mono Rock-typing is now using one of the best defensive mono-types in the game to take neutral damage from most of the tier, with Grass and Electric types not being too too common. Does not run Tera Blast.
-usually ran Tera Grass for Palafin as well as extra power to Giga Drain but I’ve seen other sets like Tera Fairy used to avoid being revenge killed by Dragapult using Dragon Darts. Doesn’t use Tera Blast.
-A sweeper that’s been exploding in prominence, I have seen both Tera Fighting and Tera Fairy on it, being able to shit on Dark-types like Chi Yu, Chien Pao, and Kingambit while losing the Shadow Ball weakness. While Tera fighting would be gone without Tera Blast, the equally as good Tera Fairy would be even more common and not be all that limited. Sometimes runs Tera Blast.
-Recently I’ve seen Tera Grass with Tera Blast be used to avoid being taken out by Palafin and threaten massive damage on Water-types and other stuff like Tyranitar, but have also seen Tera Psychic to now resist Fighting-type attacks as well as Tera Dark or Fire to give it super STAB and make it even more difficult to wall. Sometimes uses Tera Blast.
-An already controversial Pokemon due to being the upgraded Weavile, I’ve seen Tera Fighting to add STAB Sacred Sword to avoid being revenge killed by Breloom and Scizor as well as Tera Dark to just make its Dark-type attacks sting more and take neutral damage from Bullet Punch. Doesn’t run Tera Blast.
-A rising threat in the metagame, Annihilape often runs Tera Water to grant it a much better defensive typing to get a sweep going easier and be more difficult to revenge kill from foes like Dragapult and Iron Valiant. Does not run Tera Blast.
-I’ve used and seen both Tera Flying and Tera Fairy to become more difficult to KO from foes like Great Tusk and Corviknight, meaning teams hoping to use these two to stop Kingambit will be in for a tough time. Does not use Tera Blast.
-Tera Fairy gives it super STAB and I’ve seen sets like Tera Steel or Fire to avoid being KOed by Scizor’s Bullet Punch. Doesn’t run Tera Blast
-not the most common Pokemon but still dangerous to face, I’ve seen lots of Tera Dragon to give it an even more nuclear Glaive Rush while being neutral to Steel and Fighting priority yet still keep the dangerous Ice-type STAB. Doesn’t use Tera Blast.
-Often runs Tera Fight to avoid being revenge killed by Dragapult, Kingambit, Chien Pao, etc. Sounding like a broken record here but doesn’t run Tera Blast.
-Strong priority users that use Tera Fighting and Tera Steel to make their priority attacks even more difficult to stomach and are excellent late-game cleaners that can just be really strong. Neither run Tera Blast.
If you missed the point of all these examples, it’s that Terastallization makes these Pokemon incredibly difficult to deal with by giving them better defensive typings to avoid being revenge killed or just getting an Adaptability boost to make them tougher to wall. Only Chi Yu, Espathra, and Dragapult run Tera Blast, and even then they have other sets that still benefit from Terastallization so banning Tera Blast wouldn’t be a big deal. Tera Blast isn’t that great and what I expected it to be and banning it would do nothing for this issue.
This leaves the preview and limit to one Pokemon restriction. I think having all present in preview does nothing. Yes, you will see them coming, but that doesn't stop all 6 of them from having a chance to unpredictably change types and win. It's not only dangerous because you don't know their type, but it's the fact they can Terastallize any time. The best sets will come forward but that doesn’t make them much easier to deal with and teambuilding does not get any easier. I know my opponent's Gholdengo is Tera Fighting, that still doesn’t ease the 50/50 that can happen. Do I attack with my Dragon Darts assuming they go Fighting or do I click Ghost Tera Blast assuming they see Dragon Darts coming and stay a Steel-type? This will be just one of many instances of this being an issue. The most sensible option is limiting to one-type + show at preview, which is already 2 different clauses which makes it iffy to restrict, but it does reasonably make sense to solve the problem to the degree. Only one abuser and you know what's coming. However, I do have my doubts on whether this will work. For starters, it can still happen at any time. For example, say I am facing a Tera Ghost Dragapult, there still may not be much I can do to stop it going out and clicking Adaptability Shadow Ball at any moment when my opponent decides they don't need the Dragon-typing. It also still massively affects teambuilding, take Roaring Moon. Not only do I have to have insurance against standard Roaring Moon but I also need to have a method to take it on for both Tera Flying AND Tera Steel, which will strain teambuilding still. Tera makes these Pokemon effectively different Pokemon with their own checks and counters that can make building even more difficult. You have to treat Tera Flying Roaring Moon as if it's another viable Dragon Dance sweeper with a mono Flying-type. You don’t have to only be able to break Rock Gargnacl but Fighting Gargancl as well. Tera uproots one of the most, perhaps the most fundamental part of Pokemon, the type chart. Pokemon is essentially a game of rock-paper-scissors, where you run coverage and super effective moves and types to cover certain threats within a metagame. Terastalizing completely takes that away, with certain offensive threats being able to change their typing and completely alter counterplay while getting extra STAB. This is a nightmare for teambuilding, because not only do you have to stack checks for said base type, but you also have to ensure that you have room to deal with said Pokemon if it terastalizes into a completely different type. I could be wrong, that's why I still think this solution is worth trying, but I'm not entirely confident in its success. Also because most will get pissed if its outright ban or not, but if this method fails an outright ban will then be our best decision.
Overall it's fine to look at other methods apart from an outright ban or keep it the same but let's not completely alter the gimmick by locking it to certain type changes nor introducing a bunch of clauses to preserve it, the former of which destroying the purpose of it to the point where we should just ban it. I think it's incredibly broken and would prefer an outright ban that will probably end up happening but if we had to try something it’d be limiting it to one Pokemon + showing at preview, but if that doesn’t work we do an outright ban because all other options are not good. There are a bunch of deadly presences rn like Dragapult, Dragonite, Roaring Moon, Gargancl, Chien Pao, and more and I’d hope to get a verdict on tera soon as action is hold off on these Pokemon primarily because tera is just that impactful to their brokenness. I don’t want to ban these Pokemon only to reverse that with an outright tera ban but I also don’t want these threats to have long-lasting impact and heavily suffocate the tier.