Your Win Condition
You are disadvantaged until you buy Black Cleaver. The goal is to take off her passive before going for any serious trade.
General Strategy
Sejuani is a tank, which is the best class against Urgot. Be mindful of her high, surprising damage.
Trading Patterns
Use your leg cone (Q) to take off her passive (gains resistances and slow immunity). Sejuani's E (Permafrost) stuns you but is bufferable: if she E's you, press E to flip her and win the animation. You can also buffer her ultimate (R). Be mindful of her high-damage combo: Q-W-Auto-Auto-E-Auto, which can do 60% to 70% of your HP.
Wave Management
Their Win Condition
Sejuani wins by utilizing her passive resistances. She wins by landing her surprising burst combo and setting up ganks.
