Lopunny-Mega is not broken. I do not think it's overbearing on teambuilding nor the metagame. Lopunny-M is easy to stop with physical walls such as Tangrowth, Venusaur-Mega, and Slowbro. All of which are common, so you aren't forced to run random niche Pokemon to counter it. Landorus-T being the most common thing in the tier also halts this pretty well. Ice Punch does a shitton, but it doesn't want to risk the burn from Beak Blast anyways. As Jrdn said, Extreme Speed isn't too much because of Lopunny-M's insane Speed anyways. Yes, Scrappy FakeSpeed is strong, but Lopunny-M isn't too strong. I think it's a top tier threat so I will not discredit it at all, that isn't the point. Simply put, it's not too hard to handle on standard builds and isn't pushed over the edge by newfound access to moves. Therefore, I would like to second the notion to
do nothing.
Diggersby.
The premier controversial bunny. I've never found Diggersby to be broken in this metagame. Protective Pads was a neat addition, but sacrificing power for them is always a drawback, and besides that not much has changed besides metagame trends which make Diggersby worse in my opinion. Greninja-A is as strong as ever, and a lot of teams will run Grass-types to stop it (and Keldeo, and other Water-types!), and the most common ones stop Diggersby. For example, Tangrowth, which can take a Choice Band Extreme Speed easily, and can live a +2 Extreme Speed with comfort and retaliate with Giga Drain / Seed Flare. Tangrowth is just one example, but I don't find Diggersby to be overbearing. Obviously it's something to account for when you're teambuilding, but I've never found myself in a situation where using normal, common Pokemon left me vulnerable to Diggersby. Landorus-T fits so naturally on every team and it halts Diggersby not wielding Protective Pads, for example. I just don't find this Pokemon to be broken at all. I think it's the best FakeSpeeder, however, but it's still not too much in a tier where Landorus-T is the most common Pokemon and it's somewhat slow in terms of FakeSpeeding (both Porygon-Z and Lopunny-M outspeed it), I would lean towards
doing nothing, for the time being. Should Lopunny-M be suspected / banned, then it would deserve a look at, but for the moment, no.
I do think that Porygon-Z deserves to be banned more than anything else on that list. Adaptability Boomburst is so insanely powerful that you better pray that you don't lose Celesteela too early. When you consider that Timid Choice Specs sets 2HKO Chansey, Heatran, Ferrothorn (after two rounds of Stealth Rock / any other chip, but still has a 25% chance after just a switch with Stealth Rock up), Tyranitar (not SpD variants!), and the aforementioned Celesteela, you realize there's an issue. All of these Pokemon are strong special walls that keep most Special Attackers in check, but not Porygon-Z. It's even crazier when you think about how only Chansey, of the Pokemon I've listed,
resist Boomburst. Your best bet is to have a Ghost-type, of which only Mimikyu and Gengar are viable. Marowak-A, too, but that hasn't been used since the start of SM. Regardless, all of these Ghost-types are easy to wear down and check with other Pokemon, and you can simply eliminate them with your own Tyranitar (not Mimikyu). Having a Ghost-type forces Porygon-Z to think before clicking Boomburst, but that isn't always enough. I think that Porygon-Z is overcentralizing and overpowered to a point where it's so hard to play against that it's broken. You have to consider two team slots on a team to checking it, or just running your own Scarved Porygon-Z and praying for a good speed tie, that I think this should go. It also has a multitude of options from its own powerful FakeSpeed or coverage through the roof. This thing deserves to be
banned.
I think Rotom-W isn't inherently broken, but it is just too versatile and strong that makes it too hard to prepare for in teambuilding. Notice how I am only mentioning Rotom-W, as the other Rotom formes, bar Rotom-H, aren't viable in my opinion. Rotom-C may have a niche, but I've not once seen it be used. So I'm only going to mention Rotom-W, the most common, and best, Rotom forme. Anyways, back to the main point. Rotom-W has unmatched versatility, pivoting capability, and the ability to neuter a lot of Pokemon with Spore. I'll touch more on Spore in my next paragraph, but it really does make Rotom-W one of the most difficult Pokemon to effectively stop. It's so effective at doing its job, it's actually crazy. With reliable recovery in Roost or Strength Sap, it's incredibly hard to stop Rotom-W. However, I'm still not sure if it deserves to be banned. It's crazy versatile, solidly bulky, and decently strong, but it's just... not what I think of when I think of when needs to be banned in a practical sense. I can't formulate my thoughts well right now and put it into words, but I'd like to see this
suspected before taking more action. I'm interested in seeing both sides to this perspective since I think I could be easily swayed either way with a bit of convincing, since I'm torn myself. Though, I'm leaning towards banning Rotom-W only. Not Rotom-H or any other Rotom forme. They are not as good as Rotom-W, and I think banning them would be unfair. Only Rotom-W can utilize all the tools its given to an extent where it's considered questionable, so it should be the only to go.
Now, Spore. Spore is not broken. Bottom line, cut and dry. I've talked about my thoughts on Spore
here, and my opinion hasn't changed much. Here's the main point from there that I'd like to take away if you don't read it all:
I see Spore as more of a... come prepared for move. It's something like FakeSpeed, which you should account for. Neither are inherently broken, and neither are too difficult to prepare for (i.e. not using random Pokemon like Insomnia Banette or something) on all teams. Spore honestly makes the tier more fun in my opinion, and it would be a shame to see it go. I do understand why some see it as a broken move, but I'm not in that boat.
Though Tapu Koko is banned now, I still don't see Spore as broken. No Electric Terrain helped it out for sure, but it's still not broken. You have to prepare for it like every other Pokemon and although I think it's super strong, most teams run a Grass-type anyways which completely neuters it. Plus, with only one Pokemon able to be asleep at a time, it's easy to just put something that doesn't have a good matchup versus your opponent's team to sleep, then use it for sack fodder later in the match. So, Spore should follow the action of
doing nothing.
For those too lazy to read,
ban Porygon-Z,
do not ban Spore, Lopunny-M, Diggersby,
suspect Rotom-W (potentially). These are just a few of my thoughts on the metagame and the Pokemon brought up in the above post.