I've one-tricked Sej since S2/S3, and I'd like to weigh in on the rework after trying her a bit Jungle and Top today. I think she has some great goals in place to make her feel like the charge-leading war-leader she's meant to be, but it feels pretty clunky and confusing sometimes to get her there. Let's discuss abilities!
Passive - Bonus Armor & MR - I kind of like the idea here, but I don't feel it was meeting much of it's goals in either the jungle or the lane. In Jungle, it was nice but it takes too long to come back. The only time it came back up when I was farming was when I crossed from red side to blue side. For it to work in the jungle, or get any use at all, maybe down the CD at early ranks? In lane it felt like a worse Malphite passive, except instead of a slowly decaying shield when I took minion agro I lost all of my passive stats, which albeit isn't terrible but it was easy to lose the effects quick.
Suggestion? Change CD to 10 seconds at rank 1. Nerf Arm + MR if needed, that's an obscene amount at level 1, but I'd rather use a small amount more than a rediculous amount not at all.
Passive - Burst on Frozen - I liked it, actually, gave you some goals to look for to really get your damage off, it was just very difficult to use. I found myself really wanting Iceborn every game, just to give myself some stickiness. Q is a long CD for gapclosing, and unless your team has a boatload of melee AS builders you'll be finding it hard to E as much as the low CC intends. The only gripe I really had was that it has no scaling, completely destroying any
Suggestion? Honestly, I think you can leave the passive as is if some of the difficulties in freezing targets are removed.
Q - No issues. Still has a long-ass CD, but it's what I expected.
W - ISSUES. The main issue I have with it is the targets of my builds. I cannot auto-attack while W is on, and I cannot stack frost while W is on cooldown without auto-attacking. Do I take attack speed, and let it be useless during W? Or do I take a boatload of CDR, give up on auto-attacking, and spend the rest of my days W-ing? I understand that allowing auto-attacks DURING the animation will allow frost stacking too quickly in a 1v1 (or perhaps not?), but either way the ability is frustrating in it's current state. In a full ranged comp, I don't want my bread-and-butter frost ability to be this way.
Suggestion? Dump half the ability, and make the remainder an empowered auto. The first half is a side-to-side AoE, applying frost. Well, 9/10 times I'm only working on frosting one monster/champion, so that feels pretty useless to me, other than it hitting camps (for very low damage anyway). Let it be the auto reset, with the flail extending past the first minion hit, then let me keep autoattacking.
W Sidenotes - Physical damage? I actually don't mind this, it offers some difference, although I'll always miss my cheese AP / Pen stack builds. It allowed me to poke melee-tops with physical, then all-in with some magical. Precision runes OP! Also, Scaling, I'm glad the HP scaling is still here, but losing an entire ability's worth of AP scaling made the stat useless. Perhaps push some AP somewhere else, or give W some back, but putting even a single AP Glyph in now feels terrible, despite some of the kit having scaling.
E - Stacking Passive - Very hard to get off. This difficulty is split between Sejuani's W woes, and the melee-only. If your teammate has a different goal target than you, or if your entire team happens to be ranged, this is a FeelsBadManAbility. Since your E is your main CC ability, and your Q is often a gapclose, if you can't just walk into someone and get your full W off + 2 auto's (or 4 auto's...), I felt pretty useless trying to get my damned stacks off.
Suggestion? Perhaps give ranged folks some sort of ability to help you, or, give Sejuani easier tools to stack it herself. Reliance on auto-attack focused melee teammates is just too niche, Q doesn't apply frost, R after-shock doesn't apply frost, she just needs help.
E - Point and Click Projectile - Considering the resources I had to invest to get all 4 stacks onto someone, if they hopped out of sight into a bush I was nearly in tears.
Suggestion? Remove point and click, and just stun any targets in range that have 4 stacks. Most of the time, this will only be one person anyway. Keeping your mouse on that target until they have 4 stacks only to have them find a way out of vision or away from you felt bad. That used to be one of the most satisfying parts of her kit was flashing into E range when they're in a bush, using it, so on so on. This coming back would help.
R - Overall, happy with the new ultimate. Was worried when I saw numbers, but because it abuses passive it felt just fine.
Suggestion? Update tooltips to use the "Frost" and "Frozen" states, so it's clear your passive will go off.
I was a little disappointed the AP scaling has been entirely removed, I really enjoyed it back when it was viable, but I understand trying to push tanks to just be tanks. I felt I always desired more stickiness, and was drawn to Righteous Glory and Iceborn when a kit like Sejuani's should lend itself to having enough CC and initiation to do what it needs to do. Make getting Frost off less impossible/more satisfying, take some of the clunkiness away from W, and I think it'll be a solid rework. I was happy with the numbers / damage types, I love the low CD W + E to get me through clearing + teamfighting, and I'm overall pleased with the new "idea" her kit presented me, just needs some love to get her feeling like a cohesive champion again.