Health stacking and map control.
Durability and crowd control
After immobilizing an enemy champion gain defenses and later deal a burst of adaptive damage around you.
Impairing the movement of an enemy champion marks them. Your allies heal when attacking champion's you've marked.
After 10 minutes gain 8 Armor and 8 Magic Resist and increase your total Armor and Magic Resist by 5%.
Gain permanent health when enemy minions or monsters die near you.
Improved attacks and sustained damage
Takedowns restore health and grant bonus gold.
Takedowns on enemies grant permanent Tenacity.
+9% Attack Speed
Like Courage of the Colossus, Sejuani can reliably proc it for the bonus defenses and extra bit of damage.
All 4 of Sejuani's abilities can easily proc Font of Life, and because you naturally stack health the on-hit heal adds up to be considerable for fights.
Conditioning's mid-game resists make you an insane front-line tank in teamfights.
Because you naturally itemize stacking a lot of health as Sejuani, Overgrowth doubles-down on that by providing a lot of bonus scaling health based on how much health you've built.
Triumph on Sejuani allows you to fronline for you team in teamfights to absorb a lot of damage, and keep going after you pick up assists.
Tenacity allows you to stick to your target for repeated autos and help sure an [E] stun.