In short what this build is for, is a guide on how to tank with Sejuani, in contradiction to the spotlight, this guide is not for jungling with Sejuani, I have tried that before and it was decent, however I found that Sejuani as a lane tank was more valuable than as a jungler.

This guide will show you how to be decisive in teamfights and turning the odds in your favor.

The runes speak for themselves. I chose health quintessences due to using Atma's Impaler. Also the enemy will fear your amount of armor, health and magic resist early game in lane. You are not likely to be bursted to pieces and can remain in your lane for a long time. That is ofcourse if your partner knows what he is doing.

I put one point in Summoner's wrath so I can use my ghost and exhaust with an advantage.
I focused mainly on the tank masteries for defence and the ability to commence teamfights.

I start off with a Doran's shield so I get that extra bit of armor and healt + regen.
Followed by boots. Sejuani will need the speed to engage and quickly escape, since you are the initiater you will be taking the damage, I make sure I slow my enemys and escape with my Q leaving my teammates to finish off the enemy team.

I start building for Shurelya's Reverie, I start with the Philosopher's stone for the health and mana regen. Sejuani may not look like it, but she consumes a lot of mana. The passive that gives more gold always comes in handy. The thing I lack now is a bit of HP , therefore I buy Kindlgem next.

Before buying Shurelya's Reverie I purchase Mercury's Treads, this so I have more magic resist and tenacity and speed.

The next thing I buy is Shurelya's Reverie: UNIQUE Passive: Reduces ability cooldowns by 15%. UNIQUE Active: Nearby champions gain 40% movement speed for 3 seconds (60 second cooldown). The cooldown reduction on your skills come in handy so you will be able to slow the enemy even more. The active can be used to chase enemy champions or escape a gank.

Next up is sunfire cape. I start off with Chain Vest for more armor so I become more resistant, dependent on your enemy you can also choose to go for Gian't Belt if the enemy has more AP. The reason for getting sunfire cape is that it goes very well with Sejuani's W, your aoe damage will increase.

I now start with buying a Phage, this so I slow my enemys even more. After some farming I complete my Frozen Mallet. The enemy has nowhere to go with you hitting them.

I will now be starting to buy Randuin's omen. I start with Warden's Mail due to it's passive:
Passive: 20% chance on being hit to slow the attacker's movement and attack speeds by 35% for 3 seconds. As you will be taking the hits when initiating a teamfight it is helpfull that the enemy attack speed is reduced. After saving up some more I complete Randuin's Omen.
The key to teamfights is in your hands now.

You start off with your ult to initiate the teamfight and stunning the enemy team.

Passive: 5% Cooldown Reduction and 20% chance on being hit to slow the attacker's movement and attack speed by 35% for 3 seconds. UNIQUE Active: Slows movement speeds and attack speeds of surrounding units by 35% for 2 seconds + 0.5 seconds for each 100 Armor and Magic Resist. 60 second cooldown. (500 Range)

When you are focusing down the carrys you can proc the active of your Randuin's omen. Due to Sejuani's Armor and magic resist the amount of time the enemy movement and attack speed is reduced is increased.

I finish with Atma's Impaler,
starting with Chain vest so it increases my armor further and increasing the duration of Randuin's Omen's active. After completing Atma's Impaler you will lose a bit of hp from your doran's shield but the attack damage you receive in return is worth it.

The skill sequence can vary as to what I have done, however, when playing sejuani you should start with your W, you can do AOE damage and farm minions or let your AD carry get the last hits. I follow up with my Q so I can escape from ganks or hit an enemy that is about to kill my teammate. Next up is Sejuani's E skill. It does magic damage and slows the enemy.

The sequence to engage the enemy goes as follows. Your proc your W and quickly charge the enemy with your Q, followed by your E slowing the enemy immensly. You can chase for the kill or if you are low you can fall back and let your teammate get the kill.

At lvl 4 I chose my Q againto increase the damage from my charge. Next up at lvl 5 is my W so I can farm more minions or let my ad carry have easy last hits.

At lvl 6 is where the fun begins. Sejuani's ult is a powerfull stun. You can now initiate the fights and catch your opponents by surprise. I start off with my R stunning the enemy, followed by My Q > W > E, this leaves the enemy either dead or nearly dead with slows on them and the AD carry can finish them off. You will most likely not get many kills as Sejuani but you are vital to your team by assisting in kills and deciding teamfights.

from lvl 6 on out it is basicly doing what feels right, I just put down what I did but given the situation you could adapt to other spells.

The reason I use Ghost and Exhaust is due to them being upgraded by the Mastery of Summoner's Wrath. You can use your Ghost to escape from enemy's or chase them down.

Exhaust is vital for every stage of the game since you can focus the enemy's Carry and focus him down without him being able to damage you.

Sejuani is a great farmer. Due to the Q > W > E sequence you can easily clear minion waves.

Pros:
A Beefy resistant tank.
Can slow the enemy immensly.
Nice AOE damage.
Can initiate Teamfights without taking much damage.
Great farmer.
Can turn the tide.

Cons:
Is not likely to get many kills.
In the beginning Sejuani feels kind of slow.
Sejuani's Q doesn't seem to have that far a range as
the arrow suggests, I found myself against a wall most
of the time than over one.

All in all,

Sejuani is a great champion that is well appreciated by the team due to it's
assists. You are not the top killer but you will be hated by the enemy team for slowing them down and controlling them so much. In combination with the items I showed above, you should be able to win teamfights if the rest of your team keeps its focus.

Sejuani can also be used for trolling, today I was backdooring a turret knowing the enemy's Lee Sin would come at me with all he got , I easily escaped and ran off to my team. Gotta love the hate they give you on chat.

This is my first Mobafire guide ever, I don't know if I did everything right with the selections so I hope this will turn out just fine. I also wasn't sure about the name of my guide but I have seen worse xD.

Cheers to you all and lots of fun ingame!