Yeah Froslass has a lot of things that make it somewhat broken in UU. Firstly, it can Spike and spinblock; it's fast so it can quickly get the hazards up. Froslass also has the advantage of spinblocking, especially BulkyLass, of which I've used and love. It does not help that UU has shitty spinners at best; Blastoise, Claydol, and Hitmontop are all we have. Hitmontop and Blastoise have no use outside of Rapid Spinning, and Claydol is just plain pitiful. Maybe Kabutops and Cryogonal can beat Froslass one-on-one, but that's not anything to say against a Froslass ban, since the fact that you're going down to RU to get a spinner to beat it is really saying something. Other ways to prevent hazards such as Xatu are not gonna enjoy eating an Ice Beam to the face, same with Crobat and stuff. Sure, you can use fast Taunts such as Crobat or Azelf to stop it, but an Ice Beam or Shadow Ball is certainly gonna hurt. Taunt is also something. Then there's also Destiny Bond, which pretty much guarantees with Froslass you're getting a free kill. Froslass can quickly just D-Bond after its Spikes have been done, and once it dies having done its job, it will take down something with it. Also Cursed Body is really annoying, if it activates and you're running a choiced Pokemon while it spikes, Froslass is guaranteed yet another layer. If Struggle kills it, yeah you're still at a disadvantage with your team sufficiently weakened. Don't forget- two sets are possible, SashLass being a great suicide lead guaranteeing itself at least two layers of Spikes a match against slower teams, and BulkyLass too can be decent, setting up Spikes with almost as much ease while having the advantage. Froslass is literally a defining force of the tier, and is the epitome of Spikes in UU, even moreso than Roserade and Qwilfish (and Scolipede), the other good Spikers in UU. The other thing is that Froslass is so good, it almost overshadows Qwilfish, Roserade, Scolipede, etc. giving them trouble finding a teamslot. I'm not sure if it's entirely ban worthy, but it definitely has a large impact on the tier.