You get a few seconds on this boss before phase 1 starts. You can get a little DPS on him during this time, but don't blow your cooldowns because he's going to put a shield up on himself very soon. As a rogue, I used this time to get Recuperate up to give me some healing through phase 1.
When the boss shields himself, the room will fill with little sparks of light. If you hit these they do damage to you, so make sure you dodge them. They go fairly slow but you can get caught between several so it's not brainless easy. As a tip, it is much easier to dodge these on the outer edge of the room because the boss will periodically do a spreading ring of many sparks out from him and the gaps are smaller the closer you are (and if you are right on the boss, you will get hit by all of them at once! weee!).
You'll notice that some of the sparks glow and flash a little brighter than others. If you run over these sparks, they will turn into little angel dudes that look like the ones paladins can summon. DPS these to about 50% and they will cast a Charge ability. When they start to cast this, run to the opposite side of the boss so that way the boss is between you and the angel. He will intercept the charge and the hit will knock off one stack of his shield. The charge has a long cast time so you should have plenty of time to get to the other side of the boss while still avoiding sparks. As a note, the pathing is fairly generous, so don't worry if you're slightly off to the side from spark-dodging. Get three angel dudes to hit him, and his shield will be knocked off and you'll enter phase 2.
The hardest part for me was not panicking and running through sparks on the way to the other side of the boss, resulting in my death.
This phase is a burn phase. If you didn't take crazy long on phase 1, you should have no problem with it as a Rank 9 brawler. This is when you use all your DPS cooldowns. If your gear is poor and your DPS isn't exceptional, this phase can be challenging but at this point that is probably not an issue for anyone facing the boss.
However, he has two abilities you do have to know how to handle. The first is a heal. Interrupt this. Easy! The second is a ring of light orbs he puts around you (similar to the orbs around the tank on Dark Animus). Run out of these, careful to only hit one orb, has they will apply a stacking DoT for each you hit. He will stun you before he puts out the orbs, so expect him to time it right as you hit your big cooldown (because that's totally always when bosses stun you, right?).
If you've made it this far in brawler's guild, you'll probably have no problem with phase 2 and will get a win the first or second time you see it. Phase 1 is the one that involves a little figuring out.
Some more tips for players:
Specific tips for mages (I am specialized in Fire, avg ilvl 552, legendary cloak, 4P tier 16):
My armory: http://us.battle.net/wow/en/character/malfurion/aliok/advancedWoWDB
Talent Calculator: http://www.wowdb.com/talent-calculator#LKqKb3LKrKbyRCNKbzApfi
Best of luck!
Quick guide with boss tactics! https://youtu.be/OCUrWTS0tR8
In-depth warlock guide to defeating Ahoo'ru