Incorporeal

Incorporeal is a level 7 affix for Mythic+.

Up to two Incorporeal Beings can spawn every 45s, and they last for 20s. They cast a debuff called Destabilize with a 5s cast time, with the effect of -50% healing and damage which stacks on multiple applications. Note that this means two stacks will completely prevent players from restoring health or dealing damage (including from consumables) for the seconds until it expires, which can very likely lead to a party wipe.

The being can be interrupted and crowd controlled (CCed) or controlled by effects such as Dominate Mind. Long acting crowd control such as Polymorph is preferred due to their long duration. Beings have all mob types for ability requirements; and damage will not affect them, so it is not possible break a CC accidentally.

This affix is easiest solved by hunters with Freezing Trap which can be pre-positioned until the spawn area. As the cast time of Destabilize is only 5 seconds, both Imprison and Paralysis are extremely effective as they are instant cast, despite their 20 yard range. Many other classes have some kind of castable incapacitate ability, except rogues only have Blind on a long cooldown, and death knights only have the charm of Control Undead. Warriors must rely on a chain of kicks and stuns if their party is unable to assist them.