I wanted to get some Primal faction XP and lose some ladder ranks, so I decided to challenge myself to make the best mono-Primal deck possible. This was my first attempt, and it's been unexpectedly competitive so far - I'm 21-10 at the moment (rising from rank 20 to rank 4). I'm sure I've been running at least somewhat well, but I still thought I'd post the list here and record some of my logic in deckbuilding and my first impressions of how different cards have felt.
Yetipult has been consistently absurd - I think it's the main reason to play mono-Primal.
Permafrost, Polymorph, Magus of the Mist have all felt very good. Magus is pretty well situated at the moment since there are so many Stewards, Maidens, and Purifies running around. If the opponent doesn't have effective removal for Magus then it is just a huge board presence for a 5-drop.
Once you are playing Magus anyway, Unstable Form becomes very attractive. At that point I think you want Whispering Wind and Jotun Hurler, since those two cards work great with Unstable Form and with each other.
You need a couple 6-drops then to get with Wind + Hurler, and Thunderstrike Dragon is the obvious choice. I could see playing more than two Dragons since they are great in some matchups, but they can be pretty clunky also.
Cloudsnake Harrier is not a great card - the text is pretty irrelevant even with Hurler in the deck - but I think it's the best 3-drop unit you have and it's good for drawing out a Torch before playing Magus. It has felt okay in practice so far.
I'm less happy with the rest of the deck.
In theory it seems like Torgov should be good - a reasonably beefy body and Unstable, Hurler, Snowball are all great cards to discard if you ever connect. But so far Torgov has just been a 4/5 blocker. I could easily see cutting some number of these.
I wanted to try Cloudsnake Breeder out, but it has been fairly mediocre. You can spark it fairly easily with Snowcrust Yeti, various fliers, or sometimes a Snowball or Yetipult ping, but it's not an amazing payoff even then. I think you probably do want some number of early drops and Snowcrust Yeti has felt solid, but I could see cutting both Snowcrust and Breeder and playing something more defensive like Borderlands Waykeeper instead.
The deck should also probably have at least a little bit more power. You can get away with a slightly low power count because you never have influence problems, but it should still be somewhere in the 28-30 range instead of the 27 it currently is. Playing more Wisdoms is also an option to help hit 4-5 power more consistently.
The most notable exclusions in this deck are Pearlescent Drake and Cobalt Monument. These are both powerful cards, but I don't think this deck wants more 5-drops. If you want to play these cards, I think you have to take out most/all of the Unstable/Wind/Hurler/Thunderstrike package, and I'm not sure it is worth it.