Some enemies in Diablo III have a nearly-transparent, blueish dome/bubble around them; it's much larger than the Shielding bubble (with a radius maybe two or three times the height of your character), and it can pass through walls. The Keywardens have it, and I've also occasionally seen it on elite mobs. What does this dome do?

Here's an image from Diablo Wiki of a Keywarden with its bubble:

1 Answer

Sokahr the Keywarden can use several monster traits: Vortex, Mortar, Electrified and Missile Dampening.

Missile Dampening, in particular, has this visual effect:

This trait is shown by a blue dome around the imbued monster. Projectile attacks that enter this sphere have their speed decreased by 90%, making ranged attacks less effective.