Guardian

Guard allies within 350 units of you, and allies you target with spells for 2.5s. While Guarding, if you or the ally take more than a small amount of damage over the duration of the Guard, both of you gain a shield for 1.5s. Cooldown: 75 - 40 seconds Shield: 40 - 150 + 20% of your ability power + 6% of your bonus health Proc Threshold: 50 - 165 postmitigation damage

Tree

Resolve

Row

Keystone

In short

Guard allies you cast spells on and those that are very nearby. If you or a guarded ally would take damage based on level, you're both granted a shield.

Patch

16.16.1