Have not been playing UU much, but I decided to get reqs here. I think it's pretty clear that Mamoswine should be banned.
Used a team with the Life Orb variant and it was able to make progress each game, even if facing one of the few checks or a tech to slow its progress (i.e: Balloon/Shuca Cobalion), while being absolutely devastating sometimes. Mamoswine may not be particularly durable, but it is not overly challenging to get in safely, especially thanks to Ice Shard threatening a large portion of the faster metagame. The combination of Earthquake and Icicle Crash allows for it to break through just about everything, too. Fully defensive Milotic can potentially eat two Earthquakes from full without hazards up, but a Knock Off on the switch-in or some hazards being set can lead to this not being a serviceable answer either (especially if you run Adamant, which I personally did not). Golis can also stomach a few hits, but a crippling ability coupled with a lack of recovery makes it a very short term countermeasure. Weezing also can do the trick, but I find it fairly easy to wear out as well. Outside of these three and a few other uncommon things like Vaporeon, there is not much defensive counterplay to Mamoswine. This is a problem for a Pokemon as common and convenient to use as Mamoswine. As for the other side of the spectrum, Ice Shard allows for it to prevent revenge killing from a lot of faster Pokemon like Noivern, Flygon, chipped Celebi, Haxorus, Roserade, and Rotom-C. It is true that there have been more Inteleon sightings recently and Cobalion/Lucario can reliably revenge kill it, but that simply is not enough to keep Mamoswine fully in check. I feel like the overall lack of counterplay to Mamoswine in the metagame is alarming and it should definitely be banned.
Used a team with the Life Orb variant and it was able to make progress each game, even if facing one of the few checks or a tech to slow its progress (i.e: Balloon/Shuca Cobalion), while being absolutely devastating sometimes. Mamoswine may not be particularly durable, but it is not overly challenging to get in safely, especially thanks to Ice Shard threatening a large portion of the faster metagame. The combination of Earthquake and Icicle Crash allows for it to break through just about everything, too. Fully defensive Milotic can potentially eat two Earthquakes from full without hazards up, but a Knock Off on the switch-in or some hazards being set can lead to this not being a serviceable answer either (especially if you run Adamant, which I personally did not). Golis can also stomach a few hits, but a crippling ability coupled with a lack of recovery makes it a very short term countermeasure. Weezing also can do the trick, but I find it fairly easy to wear out as well. Outside of these three and a few other uncommon things like Vaporeon, there is not much defensive counterplay to Mamoswine. This is a problem for a Pokemon as common and convenient to use as Mamoswine. As for the other side of the spectrum, Ice Shard allows for it to prevent revenge killing from a lot of faster Pokemon like Noivern, Flygon, chipped Celebi, Haxorus, Roserade, and Rotom-C. It is true that there have been more Inteleon sightings recently and Cobalion/Lucario can reliably revenge kill it, but that simply is not enough to keep Mamoswine fully in check. I feel like the overall lack of counterplay to Mamoswine in the metagame is alarming and it should definitely be banned.
, but since when does Sawk resist Ice and Ground and why would Mamo not run ICrash?
Alomomola: Amazing physical bulk combined with Regenerator makes the Mamoswine matchup much easier for stall teams.
Slowbro: Another Regenerator water type that works well in many balance cores.
Rotom-Heat: Outspeeds Mamoswine and resists both of its STABs.
Cresselia: Levitate, great bulk, and recovery makes Cress a solid Mamo counter.
Suicune: Crocune avoids the 2HKO from Earthquake and Vincune outspeeds Mamo.
Gyarados: Outspeeds Mamo and only takes around half from Icicle Crash thanks to Intimidate.
Scizor: Doesn't switch into Earthquake comfortably, but resists ice and threatens Mamoswine with Bullet Punch.
I was really hoping this thing didn't drop because it sounds like it'll have a rather unhealthy presence but OU had other plans. I could see this mon definitely being an issue for all the teams running something like Golisopod or Inteleon as their Water of choice. Rhyperior is also 2HKOed by Earthquake with some chip - alternatively, you can U-Turn it, or Trick it your Choice item. 
Rotom-Wash will definitely be an interesting addition, though Mamoswine will hopefully be gone soon it will probably be able to serve as a good check. It also returns our trend of Electrics that fuck over literally all of our Ground-Types. A core I can see working is a VoltTurn core of Rotom-Wash + Noivern or Incineroar. While Noivern basically brings in Rotom-Wash against all of our Ground- and Rock-types, and Rotom-Wash brings in Noivern against Grass-Types, Incineroar can deal more damage with the combination of Knock Off + Toxic + U-Turn, not to mention being brought in via Volt Switch.
Sylveon will be a blessed addition for sure, checking Haxorus, Noivern, and several other offensive threats. More clerics are always welcome and it pairs excellently with Bronzong and Doublade. Speaking of Noivern, the Fairy + Dragon + Water + Steel cores that infested last generation will likely make a resurgence. Sylveon + Noivern / Haxorus / Flygon + Milotic + Bronzong sounds like quite the hassle to beat. Again, we are desperately lacking in actually decent Haxorus switch ins, and Sylveon at least makes it think about running Poison Jab.
I don't really have much to say here. I guess it's a better sun setter than Ninetales? Maybe? This probably won't have much of an effect on the tier, I don't see sun teams rising in popularity either. If this seems short and rushed, it's because it is, there's just not really much to say here.
