Sejuani's spell is too strong

Even if you are not running glacial or knight, she is better fit for any comp than most and it is simply because the ult is the only thing that matters. The size alone is ridiculous because it can hard cc an entire team by itself for a very long time. If that spell needed a good while to build up before it could be used AND she was a squishy champion then sure, but she is tanky enough as is to last the few autos to use it. Adding any mana item only makes it better for her.

She should honestly be a tier 5 champion, not a 4 because she is too reliable to be in the game, and in good amount, as a tier 4 for her power she brings to literally any team comp.