Yup, killed him last Monday tanking the purple one and having fire buff on pull. The 100-50% was the hardest part. Most of the damage come from his swipe (magic damage) so I saved most of my cooldowns on the 4-5 stacks.
As for setup, I went with :
- Gear : Class ring legendary, Reliquary trinket, Shade of Xavius trinket (forgot what my other legendary was) ;
- Talents : Gift of the mists, Dampen Harm, High Tolerance.
When purple does his 100% ability, use this time as a break. Once I got to 50% and switched to Shadowtouched, the fight was a walk in the park.