While Ultraxion is definitely the most unique fight for healers in this tier, Yor'sahj the Unsleeping is a close second place. The boss' abilities are simple for the DPS classes and tanks, but healers will constantly be reacting to the summoned oozes and their various effects. These globules cause us to shift our healing strategies with each new wave, and learning to handle the globules will be the key to mastering this encounter.
Every raid group is going to handle the ooze packs differently. You need to familiarize yourself with what each ooze can do, and then combine the effects based on your raid leader's preference. You'll be faced with three oozes at a time on Raid Finder and normal difficulties, with the option to kill one ooze out of each wave. On heroic difficulty, there are four oozes per wave, for a total of three effects on the boss after you've killed one of the oozes.