I've been playing the metagame for a few days now, and one thing has been really apparent to me. This metagame is not balanced... like at all.

It was a step in the right direction to ban traditional Ubers like Mega Alakazam, Mega Blastoise, and Mega Kangaskhan, but the fact that Mega Metagross and Zygarde didn't go with them is a little silly to me. Mega Metagross is the silliest one to me, as it's banned in SM OU, a tier with a significantly higher power level. Keep in mind that it's buffed in this format due to gaining stronger STABs in Heavy Slam and Psychic Fangs. Pair this with Thunder Punch to beat Skarmory and Slowbro, and Mega Metagross is impossible to wall. Zygarde is in basically the same position. It was banned in ORAS OU, a tier which I'd also argue has a lower power level than this one, when you ignore megas at least. Zygarde, unlike Mega Metagross, is at least technically possible to wall if you spam Unaware Clefable, Slowbro, and Gourgeist XL, but being restricted to such a small pool of answers is not healthy for the metagame whatsoever.

While Mega Gallade doesn't have the proven track record of being broken that Mega Metagross and Zygarde have, simple comparisons to Mega Metagross should make it clear how broken it is. Mega Gallade shares Mega Metagross' speed tier while being significantly stronger than it because of Sharpness. While Mega Metagross' bulk is what contributes to it being broken, Mega Gallade is still far from being frail, AND it has Swords Dance to make itself even stronger. While I disagree with having choice items and HBD by principle, Choice Scarf feels like the only reliable way to beat something with such a high speed tier, which is still unreliable since Gallade can just switch out.
I have way more Pokemon that I think are either currently problematic, or will become problematic later on, but these are the three that need to go as soon as possible. Mega Gallade should just get Inner Focus back, though. I feel like banning it would be sad given how it was never intended to have such a broken ability.

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This is the list of additional Pokemon that I think are currently problematic. The least controversial one seems to be Mega Starmie. I think the biggest thing that breaks it is how good of a mixed attacker it is. Flip Turn just lets it ignore potential answers, while Thunderbolt lets it beat Skarmory and Slowbro. Even if it's a little easier to wall, it'll still just pivot loop you until you die. It gets Recover and Rapid Spin to heal the hazard matchup too so like, good luck taking it out over time.

Mega Lopunny got Swords Dance, and now it just beats any team without a Slowbro. U-Turn and Scrappy buffs from SS NatDex help it a lot as well. It's broken for very similar reasons to Mega Starmie.

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I'm gonna go out on a limb and say both Greninja's are broken. Mega Greninja getting Technician seemed like a fine nerf, but boosted Flip Turns are genuinely so dumb and make it so much harder to play around. Normal Greninja can get Battle Bond boosts super easily from Nasty Plot. It forces switches super easily, so setting up Nasty Plot is incredibly easy. Unaware Clefable, Hisuian Goodra, and Mega Dragalge are all solid checks, but they are really awkward to fit in when Mega Metagross and Zygarde mandate so many physical walls to beat them. This doesn't even mention the set variety Greninja has with Protean sets either. Imagine tearing apart Clefable with STAB Gunk Shot. It's utterly disgusting.

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I remember a friend on Discord showing me a screenshot of Mega Delphox with Levitate and wondering how you switch into it. You kinda can't? Pursuit and Sucker Punch make it seem less broken, but all they really do is temper it while demanding very specific counterplay.

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Shell Smash is just super fishy and dumb, even more so on a mon with actual stats. I don't have much to say on it since I haven't seen it yet, but it sounds very broken at a glance.

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I think this is the least convincing one, but I think Feraligatr is utterly disgusting when it has boosted Scale Shots and Swords Dance. Spamming Aqua Jet with that attack stat sounds perfectly decent too.

The following is a list of Pokemon who I think might become broken in the future, but only after the prior Pokemon have action taken against them. This metagame has the potential to be really fun, but when the only powerful options are mega evolutions, it means that a lot of cleaning will have to be done in order for the metagame to be balanced. Active and consistent tiering is the best way to keep this metagame active in the long term.
Finally, I want to give my quick thoughts on the movepools and items. In terms of movepools, I think using NatDex movepools makes sense. LGPE has proven that no hazard removal can still make for a fun metagame, but having Spikes and Toxic Spikes on top of that would just be too much. I'm also not a fan of BDSP cutting so many movepools in half, so I like having more options. In terms of items, however, I just don't see the point of adding some items without adding the rest. It just feels very arbitrary to have choice items and HBD instead of all the other items.
Anyway, I hope this post doesn't come off too negatively. I think this metagame is really interesting and I want to see it shine.