Welcome to my Sejuani guide. First a little bit about Sejuani. If you chose this champion you probably meant to click on Nautilus and should rage quit to wait for another game. Nautilus does pretty much the same thing as Sejuani, except it actually works when he tries to do something.

Due to Sejuani being useless I like to put 18 points into arctic assault so it has a low enough cooldown that I can perma-spam it to stay out of team fights.

The only runes worth running on Sejuani are move speed quints so I take 30 of them. This lets you move really fast and stay out of teamfights, which you will die in because you picked Sejuani.

I like to run 1-15-8 mastery pages on Sejuani. One point in offense for improved sprint to help you stay away from teamfights.
The 15 points in defense might seem pointless* ( which is true because you picked Sejuani and are going to die), but the 3 points in Initiator help you stay away from team fights. Arguably this is still useless as you are Sejuani and will never be above 70% health.
8 points in utility are mandatory. Improved flash lets you run away from team fights more often. Swiftness lets you stay out of team fights more effectively. Improved recall lets you go back to base faster to heal (which will be all the time because you chose Sejuani) and buy items (which will be never because you chose Sejuani).

This item build is copied from the top rated Sejuani guide on the site. In reality it doesnt 't matter what you build because you are Sejuani and won't do anything useful. Don't even think about a sixth item because you are Sejuani and this will never happen.

Sejuani has no unique skills.

Bristle is your boar/warthog/battlehorse. Bristle is kind of badass. Bristle is the only redeeming feature of Sejuani.

In conclusion when playing Sejuani you should pick a different champion or afk in base for 20 minutes (you'll bring more to the team that way, because you chose Sejuani).

Also if Sejuani lives in a frozen waste land, why does she wear a bikini all the time?