So. I have been doing a little matchmaking, and although Sinnoh came just a few days ago, I am already watching a set being abused. But I will get to it later. Now, I bet everyone was expecting such a thread to pop on eventually and, despite I said I wouldn´t get involved in any more of this, This case deserves special attention:
As we can see, we got ourselves a stupid powerhouse, which gamefreak decided to give 102 base speed because yes, and to outspeed all other dragons in the tier. Ladies and gentlemans, what we are looking at is a mon that reaches 169 speed maxed, hits as hard as salamence or dragonite (Just irrelevantly tad weaker), with better stabs and a key resistance to stealth rocks, which the other 2 lack. But if you think garchomp just hits hard, you are in for a surprise. If you make easy maths and approximations, you will realize Garchomp possesses ~92% of Mandibuzz´s bulkiness (In both sides of the spectrum), which is supr terrifying for an offensive powerhouse like this one.
Moving on, Garchomp posseses a single ability in the form of Sand Veil. In such a short timespan, I already saw people spamming sub lefties garchomp under sand to try and fish those juicy misses. This specific combo turns Garchomp into one uncompetitive beast that, with its amazing speed and typing, has little to lose by spamming substitute until opponent finally misses a move. If we remove Sand Veil out of equation (Which I would vote for a ban, complex ban, or whatever) Garchomp is still a force to be reckoned with. Not only this cutie thing is able to come in safely against a lot of stuff due to its holy defenses and typing, but also has virtually no good counters, with remarkable exceptions in the form of ice fang Gliscor, Bronzong , Skarmory and Mandibuzz (Note that even these can fall to some sets, but thats not relevant here).
There are some revenge killers yes, although not in a great number. Unlike salamence or Hydreigon, Garchomp is much more sturdy against the likes of scarf darmanitan, and even lowly spatk invested HP ICE mienshao fails to get the kill, even when garchomps is subdued by rocks. Nevertheless, depending on the set, checks include ice beam starmie, scarf Hydreigon, Scarf Salamence, HP ICE jolteon, and virtually any common ice shard mon that possesses a boosting item. (Note that all these can fail if they face a sand veil garchomp in sand)
Conclusion: Sand veil should, in my opinion, be banned under uncompetitive criteria (Or unhealthy? I always mix these). If we remove this ability out of the equation, it is still really problematic in the tier, but I believe its possible to find ways to stop it.
I vote for (AT LEAST) A ban on sand veil.
EDIT: Garchomp only has sand veil in MMO.