Going to dump my thoughts on tera but I'm going to preface this post by saying I intend to vote Full Ban as my primary option. For some reason, this is enough to dissuade people from even considering my opinion on Tera as legitimate among certain crowds so this is your heads-up to stop reading. I'm going to recount my own experience from suspect laddering, 1800s, and tour games. With the lack of meaningful tour games to pull from outside of the most recent rounds of the No Johns tournament, I don't see any real reason to draw from anything other than my own experience with the mechanic. That said, experiences obviously vary so my own won't be the same as yours. In this post, I'm going to outline what I'm voting for and then explain my rationale in a two-question format.
This is how I'd personally deal with tera, not exactly sure how the second question will work in this test but I'm assuming it will have something to do with combining restrictions
Full Ban > Tera Captain > Tera Preview > Anything Else
Why I'm full ban rather than a restriction
My approach to tiering usually starts with asking myself "Does x make the better player win less", If the answer is yes then more often than not that I'll typically vote ban. In the case of Tera it was an "I don't really know". During the honeymoon phase of the metagame a little over a month ago I was having a blast with Tera but it was pretty evident that some form of restriction needed to be done, at this time I was perfectly on board with keeping it but with some restriction. Fast forward to now, I think removing it would give us the most competitive metagame while having the least amount of tiering action. I personally think in an ideal world we try to keep the number of suspects and quick bans we do to a minimum while acting on the broken aspects when necessary, and the fact of the matter is, outside of the china duo a lot of the top guys on the "chopping block" are pushed over the edge by Tera. Would pokemon like Dnite, Espathra, Garg, Ape, etc... be broken without Tera? The answer is we don't know, but, the ability to change your defensive and offensive profile into one more suitable for their game plan certainly is a notable problematic factor in all the guys I just listed. There is a reason why in the cases of Espathra, Garg, and Ape they change into better defensive types which is to minimize their counterplay options. You can obviously point out we can just ban all the brokens and re-suspect test them in the future if Tera is fully banned, since that's the reasonable response to this point I'm making. In that case, I don't think have considered the DLC season enough. In generation 8, while the tiering was considerably better than in past generations, we struggled to make a playable metagame for months because when we were just getting somewhere tiering wise we'd get dropped with a whole new batch of mons. A whole new lot of brokens were added which focused our attention elsewhere (while adding counterplay to some previous brokens). Tera has already proven that it can be the tipping point of certain mons and when even home drops we will probably have an entirely different meta that changes our priorities to the new brokens rather than retests. The thing with bans too is that there is always the next thing in the wing to take its place as a top threat, especially with newer metas. Valiant, Gambit, Hatterne, and to a lesser extent, Scizor are already annoying to deal with when they've Tera'd and they will probably only get better once we cut the top threats. What I'm saying is, the way we are approaching this can lead to us cutting a lot of pokemon which is less than ideal while in the event we do ban tera fully in the future, gives us a ton of retests to do without considering future bans as well. Which in all honesty, we do not have enough time for this given the DLC schedule. Four retests in particular is already an excessive amount. We could group mons together in a retest but that doesn't really give us the most accurate data. Even in the event we don't fully ban tera this still applies as we are going to get more counterplay but I digress. You can argue that I'm trying to jump through hoops to keep these pokemon in the metagame. Well, I can also switch that around and say we are jumping through a lot of hoops to keep the mechanic that breaks a good portion of pokemon around. Personally, I'm going to side with the option that gives us more playable pokemon and options in the builder.
While the first paragraph was solely about tiering, this one is going to be more about how Tera plays and why I consider it not particularly competitive. As I've already briefly mentioned, being able to change your offensive and defensive profile on a whim is incredible. Not just on the mons I previously listed but on just about everything in the metagame. There is very few pokemon that are bad at using Teraing. While in a vacuum, everything being a good abuser of the mechanic isn't a bad thing, the issue stems from the general lack of control the side that is not Teralizationing faces. This interaction isn't necessarily skillful and gives one side far more of an advantage. Sure the not teralizing side can "predict" the tera and play accordingly but there are also several other aspects that complicate this such as deducing what move your opponent is clicking as well the fact they can also just not tera which gives too much power to one person with the lack of skill involved. There's a lot comparison to Z-Moves in the power Tera has a singular turn and I've seen the idea that since we are okay with z-moves why not tera, but the thing is that is where the similarities stop. Z-Moves had a particular building limitation that let us adapt and build around it as most of the time the z-moves were placed on the best abuser on that particular team which the other player could use their own knowledge to figure out. This created a sort of "hierachy" of good z users that let us prep and play around the top guys while also giving us the option to run more creative sets at the expense of using it in a less effective manner. While there is obviously a top tier of tera users that you should prepare for, there's a few reasons why its a lot different than z-moves at a building level. Due to the general freedom Tera gives you in application, there's no real way to be ready for it. The example that I think is the most straightforward; Water Garg, Fairy Garg, and Rock Garg for the most part have different checks, while you can be prepared for all 3 of these on paper quite comfortably, the Garg player can still end up in an advantageous position since the way you play around each is different. This trails back to some of the different interactions I mentioned earlier and how much of an information overload tera can be sometimes. Sure you can be like "well that's garg for you", but garg isn't the only pokemon that has this sort of interaction, as I mentioned before a lot of the good abusers tend to change their counterplay to better achieve their gameplan. While Z-moves "sorta" had the issue it was less of a problem considering the general limitations and drawbacks Z-Moves had. As the age-old saying goes "You can't check everything" but with the ability to change your counterplay at will thats even more so right now. A lot of the examples I listed are mostly 1v1 scenarios, now consider the fact we play 6v6 and every pokemon can tera whenever, surely you can see where my problem lies. Just to boil this down, Tera as a mechanic offers too much control over the game to one side of the field just for clicking a button with its incredibly large amount of uses and interactions. While it is possible to play around, it doesn't change the fact that it can turn a losing position into a winning one despite the inherent lack of skillful playing for said position. Teralization (especially in its current state) acts too much as a crutch and a get-out-of-jail-free card that lowers the skill gap to the less-than-desirable degree.
Why I prefer Tera Captain to Preview
Now admittedly, posting a "ban tera pls" post is relatively unhelpful despite how much I feel this mechanic cannot be balanced or to have it in a balanced state we will have to do more than a simple single restriction which at that point we might as well just throw it out now because it's just going to cause a bunch of grief down the line. The fact is, a lot of people want to see if we can make this mechanic work because the amount of freedom it gives is interesting, despite how much I feel it's beyond the point of saving. There's a reason the test is structured the way it is. It seems this thread's favorite restriction is the Tera Preview option, mostly due to the fact VGC is currently doing it anyway. While I'm "fine" with that option, I think it doesn't really do much to affect the impact the initial turn of teralization can cause nor does it really bring the more broken users down a notch. Most experienced players already know the good tera types on OU Viable pokemon, while having the information is reassuring, you already were likely trying your best to position yourself in a while to play against those anyway. Rarely are you actually being caught by something random thats not actually meta. I feel the option of having only a singular pokemon that can teralization on any given team does a far better job bringing the mechanic down a notch. Personally, I'm indifferent to knowing who the abuser is but I do think there's some fun in not knowing who the single abuser is but just some food for thought. First off, this limits the options teralization can give you by limiting it to one member of the team which removes the problem of any pokemon having a get-out-of-jail-free card at any time, forcing both sides to play more intelligently with their Tera Captain. Additionally, by limiting it to a singular pokemon naturally, some pokemon are just going to be better at Teralizing which makes building against Tera easier since people aren't going to want to waste their captain on something less than ideal unless they are running something more on the creative side. This puts teralizing a little more in line with z-moves and what made them playable. This might confuse you why I think this nerfs some of the more broken abusers a bit. My rationale mostly comes from the fact you cannot stack all these guys on a team and expect them to be as effective. For example, you load into a game vs a garg and ape, since they are limited to one tera user that means one of them likely cannot tera (or you will know who can). This reduces the number of outcomes that can happen which balances out the control aspect I mentioned before a tad. Even if its not the perfect solution it is definitely fairer than it is in its current state. I also like the fact that this option encourages more intuitive building rather than slapping on brokens. Like I already mentioned, this makes Tera more similar to Z-Moves and in line with the general framework of why they ended up staying in SM. While this isn't perfect and some people might not like this as a solution as changing your typing is effectively better than a one-time nuke, it gives Tera some flaws that we know were effective in balancing in the past. There are obviously downsides to both options as well but I think I like what this one brings to the table a bit more for our meta when compared to preview. For the record though, if vgc continues to do the open-sheet stuff, I don't see why we wouldn't just add it to our metagames. I think the extent of "restriction" we can get away with is Tera Captain + Preview before we just give in to the full ban.
I do hope we can just outright ban Tera and move forward as I don't really see this mechanic being balanced even after restrictions but hopefully my two cents on the restrictions add something of value to future conversation. I encourage people at least take all information they consume through this thread, youtube and their own experiences to form their own opinion rather than what they are told is the right vote.
Amoonguss 
Annihilape 
Azumarill 
Baxcalibur 
Blissey 
Breloom 
Chi-Yu 
Chien-Pao 
Clodsire 
Corviknight 
Cyclizar 
Dondozo 
Dragapult 
Dragonite 
Espathra 
Garchomp 
Garganacl 
Gholdengo 
Glimmora 
Great Tusk 
Grimmsnarl 
Hatterene: 
Iron Hands 
Iron Moth 
Iron Treads 
Iron Valiant 
Kingambit 
Meowscarada 
Quaquaval 
Roaring Moon 
Rotom-Wash 
Scizor 
Skeledirge 
Slowking 
Ting-Lu 
Torkoal 
Toxapex 
Tyranitar 
Volcarona 
