Oath of Sorin

When Oath of Sorin enters the battlefield, each opponent loses X life, where X is half the number of planeswalkers you control, rounded down. You gain life equal to life lost this way.
Whenever you cast a planeswalker spell, creatures you control get +1/+0 and gain lifelink and vigilance until end of turn.
"So you've decided to condemn this plane, Nahiri. I'll make sure that doesn't happen. I will keep watch."