So I got my Coil reqs after quite some laddering, making the post reqs now
Shaymin-Sky was probably suspected for the many qualities it has. at 127 base speed, It pretty much outspeeds most relevant things in the meta, besides mega-gengar and deoxys, so Speed control is required in order to prevent it from doing it's role. Usually, this shouldn't be a big issue, as things like talonflame have such a privilege (thanks to high speed and gale wings) and yet are still tolerated, but Shaymin sky's serene grace renders it capable of shutting down the proper answer which would otherwise counter it. Your probably going to say its unreliable to bet on a 60% chance when u can simply switch out until the skymin threat is taken care off, but competitivly, even in tournaments many players choose to stay in and go for that flinch chance instead of doing the play, adding to that that skymin is mostly utilized on hyperoffense, leaving most switches risky, generating a "need" to flinch in order to win, potentially spoiling the game. That alone makes shaymin a nuissane to have on the feild, but i dont want to stress on the flinching part too much.
In terms of coverage, grass-flying hits all types except steel, which most shaymin skys run earth power for, making it really proficient at attacking and handling most pokemon on the field, earning it a solid spot in Ho teams along with the amazing speed discussed earlier. Seeing it's moves in depth, airslash has enough bp to be threatening and seed flare's power is only accompanied by a 40% spdef drop, and thats before serene grace, neutralizing spdef wall checks, notably the likes of cresselia.
An aspect I didnt see a post for yet, or I must have missed is the keldeo+skymin core. The mascot of Ho teams, the duo is devastatingly capable of punching many kinds of holes in most teams, and few threats can stand in it's rampaging way (mostly aegislash). Keldeo's quick guard ensure the priority weakness is covered (we're looking at you talonflame), the grass water coverage is capable of hitting plenty, adding fighting and flying. That's plus speed and power which are present in the stats for garanteed destruction. Tier Co-Leader Arcticblast even described the core as one of the most effective in the current meta, and guessed it still will be in the close future, when asked about it after his interview in player of the week.
A note to add is that focus sash gives it "second chances" since it's so easy to ko, which skymin appreciates heavily.
So far, we have a fast and hard hitting skymin, enjoying exellent offensive coverage, adding to it insane chances to flinch and spdef drops. However, skymin is far from flawless, and several drawbacks keep it from being broken.
It might be just me, but a criteria a pokemon generally must have when it's banned is being overcentralizing, or having a reason to be in the least. That is not the case with shaymin-sky. While it impacts teambuilding hugely, always popping out as a concern for trick room and hyperoffense and teams in general, Some threats are prioritized when adding stuff to deal with them, such as lando-T and Kangaskhan. Most teams are and should be more equiped to face the latter two than skymin. Skymins isn't a must on every team, nor is it a must to have a solid check dedicated to it. Many have also noticed it got rare usage even in it's own suspect test.
This was already stressed enough on, but Speed control almost completely shuts skymin down, not to mention makes it dead weight in a match (Thankfully making flinches 2 slow). Thunderwave just takes it's life, and icy wind slows it without mentioning hitting x4. Trick room reverses it's high speed.
Prankster and priority bypass it's great speed, which is skymin's selling point so it can't do much vs these either. Notable examples are talonflame, thundurs, ice shard users (being rare as they are), tailwind teams and even scarfers (generally lando-t rock slides and kyurem-Black ice beams). So skymin loses a lot of it's utility when it's bypassed in speed.
Frail as heck. The bulk-ish (100-75-75 isnt awful tbh) it has on paper does not match it's actual bulk in battle, so landing a hit on skymin is mostly going to hurt bad. This also forces shaymin to run a sash. Adding to this that It's typing is not impressive defensively, having 5 weaknesses (one is 4x) to common typings like fire, and the resists it has(while resisting grass and water is very positive) wont matter much as it isnt made to take hits.
Another point, and actually a kind of a reminder is that the flinch chance is still 60%. We all know numbers mean so little when scald's 30% is actually 90% , while in opposition hitting 90% moves is a rare occasion, especially when u need it most, but there is still a 40% chance not to flinch. I have actually scored nicely in games where they bet on a flinch that didnt happen. A favorable gamble remains a gamble.
The Last point I'm discussing in this post is that shaymin's traits, while being very positive, only allow it to fit in Ho teams, and perhaps balance. The limitation it has to aggressive playstyles make it less overcentralizing, less metabreaking and less relevant than things like Kangaskhan and lando, which you can slap on most teams with little worries.
Summarizing, Skymin is one of the rare viable grass types in this meta, and perhaps the only offensive one. Amazing speed and spatk (127 and 120 respectively) render it a force to be reckoned with offensively, outspeeding and destroying, while having access to spdef drops for wallbeaking, and a favorable flinch chance to shut down counters(even trick room). Fits really well in ho along with keldeo, forming a really hard to stop duo. At the same time, that limits it to aggressive playstyles/teams. It's very poor defensively in typing and stats, and becomes more of a burden than dead weigth when crippled with slowness, relies on a percentage to beat it's counters and simply isnt overcentralising to a must-ban point.
I tried to be as objective as possible in the critique because I dont have a stable vote yet, might even go abstain if i make it, leaning towards "keep"
