Picked up Sejuani. I enjoy using her quite a lot. Her W has almost no cost and no recharge time. It hits an area around her for damage based on my max and ap over 3 seconds, and applied Frost which I can use to slow and kill minions. She's got a really strong super early game, like, level 1-3 she's hard to kill solo. You'll basically trade and be near death, but you should win any fight and it works for locking down nasus early game, too.
The problem is that I don't know how to build her. I've been focusing on the HP to get the most out of my W and playing top. So I grab RoA first, starting with a Crystal for extra starting HP. thinking of swapping tat for a Doran's Sheild since it blocks damage and gives max HP, or an Ancient Coin to get extra gold. But eiter way, I got for RoA, Rylai, Iceborn, and Randiun. Not necessarily in that order. Spellblade is useful, and on Iceborn it applies a slow to an area that just adds extra to the area I'm hitting with W anyways and then my e will damage them and slow in exchange for using up frost so I can just Q into them and then w again immediately. Sejuani doesn't seem to have much bulk and goes down pretty fast mid and late game, so my kd with her is always pretty ridiculous. Large death toll, massive assist toll, decent kill rate. Cause Sejuani's slowing power and her Ult. HER GODAMN ULT FREEZES THE TARGET AND EVERYONE AROUND THEM! The freeze is more then enough for a sated devourer Yi to delete most champs an it hits everything around the target, so you can setup group freezes or use it to catch the fed person on the team and just throw everything at them after Qing to maximize stun time. It's ridiculous and I love it.
Wow, wth am I doing, rambling like a crazy man about this?
EDIT: sorry about the ramblings. It's just when I get a style I like, I tend to go into detail, as you can plainly see. I'll try to spoiler these from now on, so that anyone with anythng meaningful to say about them can still read them and no one as to deal with seeing my giant walls of rambling XD