Sejuani

Strengths

Use Arctic Assault to escape bad situations, interupt channeled spells or chase runners.
Melee allies can stack Frost for your Permafrost, keep an eye on who they are attacking.
Save Glacial Prison for encounters where you have teammates present to take advantage of it.

Passive · Fury of the North — After being out of combat, Sejuani gains Frost Armor which grants Armor and Magic Resist and immunity to slows. Frost Armor persists for a short time after Sejuani takes damage. Sejuani can damage a stunned enemy to shatter it, dealing massive magic damage.
Q · Arctic Assault — Sejuani charges forward, knocking enemies into the air. The charge stops after hitting an enemy champion.
W · Winter's Wrath — Sejuani swings her mace twice, dealing damage, slowing enemies and applying Frost stacks.
E · Permafrost — Sejuani freezes and stuns an enemy champion that has maximum Frost stacks.
Ultimate · Glacial Prison — Sejuani throws her bola that freezes and stuns the first champion hit and creates an ice storm that slows other enemies.

A suggested 5-lane lineup built around Sejuani, based on hero partnerships and role synergy — not win rate.