Decks which are strong round one (e.g. Freaks) or two - hit wins (e.g. La Junta) also do well since they can often out damage their opponents if the rounds are split 2-2. Clans which rely on close 2 or even 3 round wins (e.g Roots) may struggle if their Frozn opponent hits hard twice.
Clans with a strong DR / SOB card will also do well, since they can almost certainly force a 2 or 3 round win
Well, SOB and SOA always do well in stopping cards/clans that rely heavily on their Ability/Bonus. At the moment, the clan is still developing, so it's tough to see things that they're going to be weak against in the long run other than Soa/Sob.
As of right now, they lack heavily in damage, the highest being 5 dmg from their 5 star, Ayah, which their bonus does help them with mildly, but strong enough DRs can really make them do minimal damage. Paired with their current lack of Poison, lack of +Life Cards (besides Tiwi ld), and lack of their own DRs some strong life altering clans could wreck them pretty hard and fast.
So Sakrohm, Freaks, Jungo, Pussycats, Nightmare, Piranas, Gheist, and Roots all seem like they'd be strong at facing them
The Frozn are a powerful but predictable clan. Load up on SoB (I prefer Nightmare for this) or strong DRs with attack manip (Montana or Uppers) and you shouldn't have too much trouble with them. Try a Montana DRs/Nightmare split for a deck that's going to be hard for your opponents to play around.
Theoretically any clan with sob/power manip is a "counter" to frozn. Most all-stars can close the power gap with them (obvious exceptions being mikaal). Ulu is another example as many of them can reach 10power, which is at the worst a tie with them. If all else fails, use atk manip.
Long story short: the only thing that isn't good vs them are the clans w/o any form of offensive manipulation.
Actually most clans do well against Frozn
Dmg/life clans can hit them hard on their non-revenge rounds
Power/Attk clans demolish their non-revenge rounds and can tie the gap when they are on revenge
SOB destroy them completely...especially Nightmare
SOA isn't as good against them as everyone thinks...Revenge rounds they demolish SOA, especially Roots
Of course in a half deck it all depends on their paired clan
Trippie is right, I think the idea of versing Frozn is to out damage them in a split 2/2 (2 rounds each) match, having DR to nullify their big round on command (or force their hand by threatening a block round 3/fury round 4) is the key. Clans like Uppers or Sakrohm would suffer because Frozn have the ability to throw a round to set up a big round 4.