https://www.youtube.com/watch?v=05XZw3KBo6M
"While many of our class updates set out to sharpen the distinct identity of their rosters, this is especially the case with tanks. Initiating teamfights is a responsibility many tanks share, but when initiation works and feels the same across these champions, they start to become interchangeable. Sejuani, Maokai, and Zac are three champions who struggled from this. We've added unique mechanics to each, giving you reasons to master them separately or choose them specifically.
Sejuani
Sejuani has the potential to be both barbarian warleader and heavy cavalry, but falls short of either. She’s defined almost entirely by Glacial Prison, whose teamfight-turning potential has come at the expense of satisfying power in the rest of her kit. We’re breaking Sej out of her ult-bot status and giving her more impactful things to do when skirmishing alongside her tribe.
A redesigned Permafrost comprises the bulk of Sejuani’s combat contributions and makes her the warleader she was meant to be. Passively, Sejuani and her melee allies apply Frost to enemies, and unlike Braum’s passive, Sej doesn’t need to be the one to start the stacking. Once a target’s reached max stacks, Sejuani can point-and-click stun them with Permafrost. Should she attack a frozen target, she’ll shatter them for major damage. Sejuani is at her strongest in 2v2 or 3v3 situations where she has the best chance of Permafrosting every enemy encountered.
Most of Sejuani’s other skills are getting updates as well. Frost Armor now protects Sejuani (well, her boar) as she charges into battle, granting bonus resistances and slow immunity. Flail of the Northern Winds Winter’s Wrath is a two-part swing/slam combo, letting Sejuani strike and stack Frost in any direction while Bristle continues to move around the battlefield. Glacial Prison no longer stuns the entire enemy team, but turns the battleground around its explosion into a slowing zone that gives Sejuani’s warband time to get into Frost-stacking range. "
Solcrushed, Game Designer