WoWDB

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.

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. 

Phase 2

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:

• DO NOT ATTACK AHOO'RU before the fight begins.  He will heal back to full when he casts his  Divine Bulwark.  Don't waste your trinket/cloak/etc procs on him, save it for the first angel.
• Pre-pot!  Buy a bottomless potion from Quackenbush (H) or Paul North (A).
• Activate the first Avenging Angel as quickly as possible, then toss a few DoTs on it.  Activate the second angel as soon as you can, tossing DoTs on it while stopping DPS on the first.  Repeat for the third angel.
• Because of the positioning requirement and timing - and RNG - it is not recommended to cause more than angel to Charge at a time.  I was very, very lucky in that I'd obliviously managed to stack the angels in pretty much the same spot!
• Blow every last DPS CD that you have for Phase 2.  Don't use a GCD to regain HP unless you absolutely must.  Hopefully, your dps potion is or will shortly be off cool-down at this point.

Specific tips for mages (I am specialized in Fire, avg ilvl 552, legendary cloak, 4P tier 16):

• Ice Block will not protect you from the sparks of light traveling around the area. :(
• Save your Blink for if/when you are surrounded by several sparks with no clear route to avoid them.  DO NOT USE BLINK JUST BEFORE PUSHING AHOO'RU INTO PHASE 2.
• If you are in position, perform a full Invocation as the third angel is casting its charge.  You won't have the time to do this after Ahoo'ru's shield breaks. DO NOT CAST INVOCATION AGAIN EVEN IF IT FALLS OFF.  You'll be wasting precious seconds.
• Cast  Mirror Image right before or as Ahoo'ru loses his shield and run away from them!  This way, he places  Divine Circle on the copies and you are safely at a distance to begin killing him as fast as possible.
•  Time Warp god.
• IMPORTANT:   Counterspell THE HEAL.  AN INTERRUPT FROM, SAY,  Dragon's Breath WILL STOP HIS CAST BUT AS SOON AS HE RECOVERS HE'LL BEGIN CASTING THE HEAL AGAIN. (sorry for yelling)
•  Alter Time your very good friend.  For fire mages, have the Heating Up and Pyroblast! buffs on you for max effect.
• For fire mages, get in a couple instant pyroblasts then cast Combustion.  The encounter is very closely timed, so saving Combustion is fairly pointless.
• Blink out of Divine Circle.  /cheese
• Ahoo'ru occasionally knocks back, so be ready to keep the dps steady by using an instant or castable-while-moving spell.

My armory:  http://us.battle.net/wow/en/character/malfurion/aliok/advancedWoWDB

Talent Calculator:  http://www.wowdb.com/talent-calculator#LKqKb3LKrKbyRCNKbzApfi

Best of luck!