I have been very
Pro-Ban on Yanmega for a while now, as I don't see anything of value that it adds for the tier besides a very frustrating HO goon. I made a post in the main metagame discussion about why I thought Yanmega was the most constrictive element to play against on an HO team composition, and I still think all those points stand, but even more so now with the banning of Thundurus, which served as a decent way to finagle your way around a late game Yanmega. I still think that being able to just click an extremely powerful STAB that does massive damage unboosted, and then getting a +1 boost just from clicking it is insane, not to mention not needing to worry about speed because it's already covered by your ability. Yes, you do run the disadvantage of needing to run an item other than Heavy-Duty Boots in order to get that boost, but on a team structure like HO, which actively attempts to deny hazards at all costs through the use of Taunt, there is a very distinct possibility that Yanmega doesn't have to worry about taking any form of chip damage coming in. And even if rocks do go up, you have options in Tidy Up to remove them, or you can just not care at all about the chip damage taken, because Yanmega is still relatively bulky at half health against the moves that matter, those being priority. You have a couple of options in that department, you can run Sucker Punch Bisharp which, without Tera Dark, doesn't even have favorable odds to KO after rocks are up. CB Entei rarely KOs after rocks chip, and needs Tera Normal for the guarantee. CB Crawdaunt does have a guaranteed OHKO on Yanmega without the use of Tera, however, I hope we can all see the pattern here of needing to expend some sort of Tera Option, or locking yourself into priority, which by definition is a weaker move fundamentally. You know what loves taking advantage of your inability to output good amounts of damage to setup and sweep the rest of your team, literally the entirety of our pool of HOers. Locked into E-Speed, well now your getting setup on by the likes of Bisharp or Revavroom, Aqua Jet gets used by DD Mence, Feraligatr, or Gyarados, and Sucker Punch, while the least directly abusable of the bunch, still has the chance of being Encored by Maushold. It’s not so much the core of Yanmega that is considered broken, but the facilitation that it gives its allies and vice versa, and how even if you do play correctly and are able to preserve the right counterplay throughout a game, you can lose that key part of your team structure to a 30% secondary effect. Yan has essentially flawless coverage as well, with its STABs + Tera Blast Ground having at least a neutral, but usually super-effective option against the entirety of the tier. Now I'm not saying that Yanmega by itself is broken, but what I am saying is that, like Blastoise, it enables other elements of HO to a tremendous degree, while still serving as an easy wincon if given the opportunity, enabled further by enough bulk and of course, flinches. Yanmega exists solely for HO, and I think its removal will make playing against it feel a lot more fair, there are already plenty of haxxers on HO between Yanmega, Bisharp, and Revavroom, so I really don’t see an issue in removing one as unique as it is in its role of proactive setup.
Just to make sure I’m not editing over blind speculation, I’d like to provide some calcs and replays in order to hopefully ascertain my point better. And just to preface as well, pretty much none of Yanmega’s checks, especially Cyclizar, cannot switch in hard to a Yanmega Bug Buzz, which again is different from other banned special setup sweepers, who could only hit Cyclizar once before being D-Tailed out. Anyways, onto the calcs,
252+ SpA Yanmega Bug Buzz vs. 104 HP / 152 SpD Assault Vest Cyclizar: 115-136 (37.4 - 44.2%) -- guaranteed 3HKO
+1 252+ SpA Yanmega Bug Buzz vs. 104 HP / 152 SpD Assault Vest Cyclizar: 172-204 (56 - 66.4%) -- guaranteed 2HKO
+1 252+ SpA Yanmega Air Slash vs. 104 HP / 152 SpD Assault Vest Cyclizar: 144-171 (46.9 - 55.7%) -- 75.8% chance to 2HKO
Like I said, can’t switch into a Bug Buzz at all, especially with rocks up. But lets say best case scenario, you sack some team member who is already low to the Bug Buzz and are able to get into Cyclizar with no prior chip damage occurred. You now run the risk of getting flinched for a light 50% on average, which I should inform you has the exact same chance of flinching as Scald does of burning. So now what, you can hope they click Bug Buzz and defensively Tera to Dragon Tail it out, or you switch out into another sack and run the same problem again. Of course, this is all very much speculative and rather cherry-picked to my point, but over not even that many games this outcome will happen, because once again, this is about as likely to occur as a Scald burn. Cyclizar is also one of the more relevant and frankly better checks to it thanks to Regenerator, but again that chance for flinch, and sometimes more frustratingly the chance to miss Dragon Tail or Draco Meteor, means that the chance to have to randomly sack another part of your team into a matchup that really depends on you keeping as many options in the back as possible is more than likely. Cyclizar has also seen a downtick as of late in usage, meaning that Yanmega has more rain to do as it pleases. The next most viable option would probably be something like SpDef Hoodra or Empoleon, both of which are not huge fans of a Tera Blast Ground to the face.
+1 252+ SpA Tera Ground Yanmega Tera Blast (80 BP) vs. 252 HP / 252+ SpD Goodra-Hisui: 216-254 (59.3 - 69.7%) -- guaranteed 2HKO
+1 252+ SpA Tera Ground Yanmega Tera Blast (80 BP) vs. 252 HP / 252+ SpD Empoleon: 284-336 (76.3 - 90.3%) -- guaranteed 2HKO after Leftovers recovery
Once again you can Tera to fix these problems, but Yanmega also has the quirky little option of just clicking Protect for shits and giggles and seeing what happens. Also, again, if you’re having to spend your Tera in order to account for one option, which can be very easily exploited by the rest of an HO team, you’re not necessarily winning the exchange in the long term. But enough with the theoretical aspects of my argument, let's look at some actual replays of Yanmega doing Yanmega things.
I present to you one very, very, handpicked replay of Yanmega working its magic, and the other three are from SCL.
https://replay.pokemonshowdown.com/gen9ru-2234795881?p2
With an endgame of boosted Tera Fairy Cresselia, which, kind of a weird Tera but whatever, you would think there is absolutely no way that a Yanmega could win, but it’s truly a miracle worker, snatching not one, not two, but three flinches, followed, of course, by a crit in order to win the game. Again, super handpicked to prove my point, but like, this is essentially the worst case scenario.
https://replay.pokemonshowdown.com/smogtours-gen9ru-793317
Pre-Thundurus ban, but I still think it’s relevant to Yanmega’s case. Elodin is able to get up rocks with Lycan while crucially denying opposing rocks from Hippo, granting extra longevity to Yanmega throughout its role as an early breaker for the rest of the team. Yanmega is switched in on a chipped Slowbro, and Xavgb switches in Klefki as his Bug Buzz absorber, and Yanmega gets the +1 boost. Elodin decides to preserve his tera here, but even with the lack of Tera Blast Ground at his disposal, Yanmega is able to put in massive work, getting rid of a potential T-Wave spreader in Klefki, getting a timely flinch on the Thundurus to deny a Volt Switch and momentum in Xav’s favor. Elodin is able to switch in and Tera Feraligatr because of this momentum, setting up a SD, removing another paralysis spreader in Thundurus, and dealing massive damage to Slowbro as well as forcing a Tera on it, which loses the game in the long term, as there is essentially nothing remaining on Xav’s team to switch into the STAB combination of Armarouge. While Yanmega didn’t really take on the role of an end game sweeper here, it was able to pull off some Yanmega shenanigans to gain momentum in Elodin’s favor and eventually win him the game.
https://replay.pokemonshowdown.com/smogtours-gen9ru-797405
While Django doesn’t win this game, Yanmega is able to put up a theoretically great performance as an endgame cleaner here. After Gweezing is sacked to get rid of rocks, Yanmega comes in and is able to boost up on a switch to Hippo. I would say that this endgame is sort of a throw by Django, as a switched in Reuniclus is somewhat obviously going to tera. Two Air Slashes won him the game, although fairly he wasn’t sure what exactly the tera was. But that’s sort of the purpose of having Air Slash, it’s a decently powerful move, doing 40% to Reuniclus that has a 30% chance of winning on the spot. Django had a potential three different opportunities to flinch here with Yanmega, giving him a 65% chance to win if any flinches happen, and while he doesn’t get the luck he needs, just having an option that has decent enough bulk to get past its checks more likely than the toss of a coin flip is silly to me. Again, while Yanmega doesn’t win, it had ample opportunity to do so if played more optimally. Kilowattrel in the back would eat one up easily enough, but again the odds would be more so in Django’s favor with a flinch chance plus the 70% accuracy of Hurricane.
https://replay.pokemonshowdown.com/smogtours-gen9ru-804146
Final game, but once again I think it was just kind of a throw from TheFranklin here, as Yanmega had a great opportunity to go off here. On turn twelve, if Yanmega had switched in over Terrakion, it would have gotten the boost off of the most likely SpDef Hoodra that switches in. Assuming max special bulk, Hoodra is taking around 65% from +1 Tera Blast plus Bug Buzz chip. I’m not entirely sure, but I assume that this is running Dragon Tail, so after a 90% accuracy check, which missing loses the game immediately, you lose the boost and take roughly 20%, however you don’t lose Yanmega, which is important. Switching into Maushold is more beneficial, as you certainly pick up a KO with Population Bomb, but Terrakion is also good as you get up rocks with Terrakion, limiting Hoodra in the future. Either of these paths give you a much easier path forward to winning thanks to Speed Boost, and while winning is not a guarantee, you have a much more clear path forward to winning. Even being down 3-5, Franklin had a very real chance to win with Yanmega because of Speed Boost.
TL;DR Yanmega is dumb and I don't like it. It promotes dumb luck over time, has a proactive way to setup which demarcates it in a very special spot for HO, its removal would make HO not so frustrating to play against and there is no real replacement for it on the structure. It also has pretty flawless coverage into the tier, only having a few real checks without the use of tera. Please don't give me any crap about Chansey, that mon is garbo and gets setup on a Bishillion times by every other aspect of HO. Yanmega adds pretty much nothing to team compositions besides HO due to other options having continual use over a game instead of a one time burst. Finally, even though Yanmega is pretty silly just by itself, it is more so the ability to almost always guarantee a sack during its setup, followed by a chance to get rid of any checks with luck, facilitating the rest of HO that truly makes it the dumbest mon in the tier currently for me.
will be enough to fix the problem of hyper offense and how it can steal games so often.
the best wall for 
switches in and threatens with an ice beam/surf
threatens with draco
Clicks shift gear and assuming no double flinch kills with gunk
Threatens with electric move and takes nothing
More niche but can twave and 4hko with hslam/iron head
Cm sets set up on it, but if its not 
with a flinches yanmega can break thru
clicks mirror coat/ice beam
Spdef 
To be honesty this is a fake check it does nothing to it.
can ice beam it
clicks draco, whilst bulky 
into range of everything. Alternativly 
, 
ect as well as hazards can chip phazers like 
into range of 
losing its ability to beat 
. Overall I do believe that forcing teras is benificial to the hyper offense team.
and 
was in ou a few months back. Ideas like tera fighting, tera fairy, tera fire, sub and more could work given the right innovations and support.
snow but thats fake anyway) whilst also having an fsight+hazards angle for bulkier teams with the only insta lose mu being 
+defog+
