Masteries are Tank AP oriented. Note that: - Expose weakness is good for we are support, so it helps the ADC - Insight makes exhaust + ignite refresh fast (179 sec). The ennemy will love it. - Courage of colossus is perfect for engage with Q (or R)!
We have no Flash, so Q is our flash / first spell. But we can wait to improve it. W is the most important spell, for it is the one who makes damage, we improve it in priority. E dont really need improvement in early, so we keep it for late.
The start items will give money and enough sustain for early game.
The core item is very balanced and I suggest you to follow the specific order of situational items. Of course, depending on the money you have, you may buy more or less at each time.
1- Boots and chrystalline bracer. So, Sejuani will run and not walk anymore (lol), and with a little health+regen, that we will transform in warmog later.
2- Bami's Cinder and Chain vest. We start the Solar cape here, but depending on the money, you probably will have to make those inbetween.
3- End of Solar cape. At this moment you should be around lvl 7-9, and if you start the warmog now, you won't have the 3000 minimum health required for the warmog passive. Also, having some magic resist is a good thing, so you can start roam and help mid if necessary, so we go Negatron coal -> Wit's End first.
4- Finish the warmog. You should be lvl 12-13 (more or less).
5- Now we are tanky enough, we need more damage, so priority to CD reduction: we go Nashor's Tooth to reach the 40%
You can sell the ancient coin now, because you will need the space in the inventory.
6- Now we go magic penetration: finish the sorcerer's shoes and make haunting guise. At this point, you'll get 38 magic penetration + the Wit's End bonus... Try it, you'll love it!
7- Finish the Liandry's torment : the passive is quite good with sejuani spells (doubled)
8- Your stuff is full. Go Elixir of Iron with extra money.