Affliction Warlock mage tower guide.

This is the healing tactic.
I write a bit throughout the video. But basically: Bring a flask for some int, bring a potion, I brought unbridled fury, and bring drums. I forgot drums and forgot to use my unbridled fury, but it will only make it even easier.
What you wanna do is use your portal and gateway to keep distance from adds and mini-boss. Hands should be focused and you should swap your unstable affliction to it. We're cheesing the fight a little bit by doing the healing tactic. Don't focus too much on the main boss during intermission or even during the final phase. This is about survival and not a damage race.
What I did was try to completely forget about the main boss during the intermissions and focus solely on the adds. Try to bring the adds under the boss by moving to the opposite side when you can see their spawn location, and then use seed of corruption on the boss which will spread to the adds that spawned and likely damage other adds too. This also makes it so the adds are better stacked and you can vile taint the boss + a few packs of adds.
Basically forget about the main boss until last phase, deal damage as you're comfortable, but it's not important at all. Focus on adds and karem. Focus on staying alive. Keep slow on Karem at all times, and at the final phase you wanna burst him down as fast as you can. Use all your CDs on the mini-boss not the main boss. When he dies there will be no more hands, and you will only have to deal with the adds, the soak and the main boss. Which is no issue at all with all the defensives we've got and self healing.
Keep corruption on adds by using seed of corruption, do the same thing you do during intermission by trying to stack them up neatly. Use vile taint here too. But we're simply using seed of corruption for the healing effect on drain life, and using soulburn along with that to grant us a shield that protects us from the main boss's 500% damage increase when karem dies.
As you see in the video it's no issue at all.
Remember you can use your pet to soak the pools.
Best of luck to you.