I've played a few games with her now (all in the top lane, can't speak for the jungle), and have tried out a couple of different builds, here are my thoughts in what I feel are the order of importance:
> **W - Winter's Wrath**
My favorite part of this ability is the fact that you can use it on the move, you don't need to stop and cast it, and it makes Sejuani feel like a really mobile character now because of it, even if she doesn't move around quite as much as other characters do.
What really bugs me about this is how damn long it takes to finish, you can't do anything other than cast your Q (which feels good, like Sejuani and Bristle are working as a team) until the second part finishes. You can't basic attack, cast E or R, and you can't activate items, and that makes the ability feel really clunky to use.
I'm not sure how to solve this. I really like the second part of the ability in theory, and it feels good to hit it, it's just that the inability to take action for half a second really blows. Perhaps each portion of the ability could be activated separately? I'd really like to be able to aim each part of this ability individually anyway just for flexibility's sake.
The first swing feels a little long-range, by the way, perhaps reduce it a tad. (there's like, 50 distance difference between the first and second portions it feels like, the only difference is the hitbox and damage)
> **Passive - Fury of the North**
I'll be frank, the numbers on this are probably going to need to be toned down a bit.
The sheer amount of resistances this provides: [100% total Armor + flat 100] Armor and [100% total MR + flat 100] Magic Resist], especially when combined with the Unyielding and Fearless masteries in Resolve (+5% bonus, and +10% total respectively), makes me feel kinda dirty, though it is really fun to make lane sized puddles with Iceborn Gauntlet.
Also, the bonus damage on attacking stunned targets is.... excessive.
Perhaps triggering Icebreaker could deal reduced damage, but activate Frost Armor? Obviously, this is assuming that Frost Armor's values are lowered some, but I'd gladly trade some of that up-front burst for the extra resistances and slow immunity Frost Armor grants in the middle of a fight (which would help contribute to the "mobile" feeling without actually granting extra mobility).
> **E - Permafrost**
This ability feels awkward. It has a 1.5 second cooldown, which is to say no cooldown, but the fact that it has such a large range and you need to target your opponent is... strange.
Also, the indicator is --**really**-- hard to see for both sides. Consider making it brighter please, it's an important part of combat.
I enjoyed using Permafrost ("Cold Snap" makes more sense as an ability name, but whatever I suppose) on her current kit, it was one of her little high moments she was allowed to have (since her ult was so darn strong), so I'm kinda sad to see it go.
I feel like the stun is currently too easy to get off, even if it's just me hitting someone, but the cooldown between stuns is very high, so I feel like I don't really contribute much after that in fights (especially since most people are out of my reach).
I would really like the old version to return, Sejuani singling people out is really strange to me, even if it does make it easier for her to proc Icebreaker, but the AoE version gives interesting choices in regards to timing and target selection, whereas the current one you basically use whenever you can, there's not much nuance there. Additionally, putting an actual cooldown on Permafrost allows stacking again sooner than the current model, which would give people something to look forward to, as well as add tension in the back of people's minds ("Sejuani used Permafrost just now, we have a bit, but we'd better do something about her before it comes back up!") and introduce a window of power.
> **R - Glacial Prison**
I actually enjoy this more than the current one by a large margin. It's less impactful, but up more often, so I feel like it's really a part of my kit that's at my disposal, but no big deal if I wiff it sometimes (aside from the embarrassment). I don't really notice the storm's effects much, so it's kinda meh, but the ability feels good, so I'm happy.
> **Q - Arctic Assault**
Not much to say here, nothing's changed. I have no complaints, other than noting that this still does magic damage, which is weird. I like that you can cast this while using your W, it feels fluid.
So there you have it, agree, disagree, do as you wish, these are just my thoughts and opinions on the subject.