Heroic Lei Shi; Scary Fog?

[Mootykins]

My 25m guild is about to start H Lei Shi attempts tonight and I'm having trouble figuring out exactly how Scary Fog works and how to deal with it. Anyone with some experience able to inform me? Again this is for 25m, so I'm not sure if there's any major differences between 10m and 25m for this specific mechanic.

[Squirl]

I don't know the best strat for 25m. I heard most run a third tank.

As far as how it works: when you pull Lei Shi, she spawns a large circle around her. People outside that circle gain stacks when her Scary Fog ticks (~5s tick; DBM has a timer) and people inside do not. The stacks cap at 20.

People with stacks get a graphic around them. Anything inside that graphic (friend or foe) takes 10% more damage per stack. The stack is an increasingly heavy DoT on the one with the scary fog, but only a damage taken modifier on others inside the graphic. The damage effect does not stack with multiple people; it chooses the highest one and is only affected by that one.