Well, the dark elves have Tramaria that is immune to freeze and other CC effects. Demonspawn has Chalco, Shadowkin has Jingwon, Dwarves has Granyt, and Undead has Fabian. There's also the epic free champ Dark Elhain that instantly removes freeze.

I'm sure that there's 1 or 2 more out there as well but those are the ones that come to mind.

I have heard that team referred to as the "Full Christmas" and it has become increasingly common, especially in 3v3 Defense, but it is rarely super fast. 

I build my PVP toons with relatively high Res, so I target the "Full Christmas" with this team:

Armanz (Lead for Speed Aura) , 310 speed, 1 turn SS, Res is only 374 so he can get frozen after initial turn

Krixia, 397 speed, 729 Res

Padraig, 398 speed, 663 Res

Marius, 307 speed, 505 Res

Krixia & Padraig are never frozen, but Marius will occasionally be frozen by Padraig's Passive Buffs or Padraig's opening A3.  If that happens, I don't use Krixia's Base A3, instead I flip her to Alt and use the Alt A3.

I don't think I have ever lost to a "Full Christmas" Team with this setup.

As long as you build your toons with at least one turn SS or solid Res stats, this team could be replicated with Fabian in place of Krixia and almost any TM Booster for Padraig.       

Yeah, tag is where I mostly see it, so not a major priority.

We had a tough one in our opponent's stronghold this siege, but one of my clanmates managed to get it

I waa annoyed about Ash'nar, since Tormin's wording specifcally says he attacks when a frozen enemy "TAKES DAMAGE" from burn, on the verge of making a bug report, but a clanmate pointed out to me Tormin has always been that way, even if you have block damage in place

Just pull Siphi and then lockout with Fabian.  😃 

I actually have Siphi. I didn't realize her passive also had a chance to cleanse freeze. Derp.

Yes and she places block debuff 1st so no getting Tormin'd. 

....but very susceptible to Supersonic. 

Yes but probably no Supersonic in the specific team trying to counter.