A few planeswalkers to start with (Lannisters)

 Alright let me begin with 2 of my favorite characters in A Song of Ice and Fire. I am not entirely sure if people will manage to find spoilers in these, as I haven't even read the books myself either. I just tried to collate all the information at hand (from all the television series) in my mind and "draw" some Magic the Gathering-style abilities.

Cersei, is a really powerful character but just so it happens almost every time her grand plans backfire, because of a slight miscalculation from her part. Her first ability reflects exactly that. Her second ability shows that in order to gain an advantage, she won't hesitate to suffer losses of her own, sacrificing anyone for her cause.
Finally, her ultimate ability enables her to achieve something extraordinary, but with a huge cost. I believe Cersei perfectly fits the White/Black (Ravnica's Orzhov) character. Still, this is draft work, I'm not 100% satisfied with her.

So, Tywin. I focused more on Tywin's character in his early days of power, making the riches from his lands, his battle tactics and finally the rallying of his Knights around him, allowing him to amass a huge powerful, heavy cavalry army. 

He has the speck of black in him, because he will do anything to gain power. Targeting creatures manipulating their combat damage and resource control, also fits the Orzhov way of thinking.