Maybe I'm silly for not catching onto this, but...

After you kill the Avatar of Hakkar[which you summon by using the egg] he drops "Essence of Hakkar." Pick that up and right click it in your inventory to fill the egg with the Essence of Hakkar.

This is part of a long chain quest designed to familiarize you with Zul'Gurub and the Zandalar Tribe. Much of the rewards are decent for their level. The Faded Hakkari Cloak is only slightly worse than everyone's favorite Hide of the Wild. Definitely a worthwhile chain for someone that doesn't want to shell out for the Hide.

Here's the full quest chain:
- Screecher Spirits(Feralas) - https://classicdb.ch/?quest=3520
- The Prophecy of Mosh'aru(Zul'Farrak) - https://classicdb.ch/?quest=3520
- The Ancient Egg(Hinterlands) - https://classicdb.ch/?quest=4787
- The God Hakkar(Temple of Atal'Hakkar) - https://classicdb.ch/?quest=3528
- The Lost Tablets of Mosh'aru(Eastern Plaguelands) - https://classicdb.ch/?quest=5065
- The Final Tablets(Lower Blackrock Spire) - https://classicdb.ch/?quest=4788
- Confront Yeh'kinya(Tanaris) - https://classicdb.ch/?quest=8181
- The Hand of Rastakhan(Stranglethorn Vale) - https://classicdb.ch/?quest=8182

PLEASE NOTE - If you wipe during this encounter, you will NOT be able to do it again until the instance is reset.

The short version:&nbsp Enter the temple, take the first hall to the left, this twists around and around and up.

Keep totally right until you find a room with a gate on either side and a skelly in a ring in the center.&nbsp Four fires burn on the corners.&nbsp Clear everything.

Use the egg, this spawns the event, kill everything you can as fast as you can, focus on the flying snakes, take their blood and put out the four fires.

This will spawn the God Hakkar's avatar, defeat him and take your prize.

Notes: We did this with 1 shaman, 1 hunter, 3 rogues from level 49 to 60.&nbsp We all but wiped and the gates opened back up (one rogue vanished).&nbsp We came back in and aggro'd the mess, pulling it outside the caged area and locking one rogue inside.&nbsp We defeated him anyhow.&nbsp The hard part is the endurance match!

actually need to make a correction, seemed like a good tip before I did the encounter, then when we went to start it, realized this was not true. You need to use the egg in the room where the skeleton of the avatar is in order to start the encounter, and then the mobs start spawning. Unless it was meant that you need to clear all the mobs around the area.

This encounter is VERY hectic if you aren't well organized, so make sure you brief everyone before using the egg.
Change the loot to free for all(thanks to the second post) and make sure one person is in charge of getting the blood and extinguishing the torches. The blood drops from wyvern looking creatures called Hakkari Bloodkeepers(https://classicdb.ch/?npc=8438) that spawn one at a time. there are also several non elite venom spitters running around, that will quickly target your priest/healer, so have at least one person assigned to pull these off of them. Also, during the encounter before Hakkar is summoned by putting out the four torches, there are elite dragonkin called Nightmare Suppressor's (https://classicdb.ch/?npc=8497#00Rzc) that spawn and try to prevent you from summoning the avatar, they also start a "drain soul" like animation on the Avatar, but I didn't really notice if it was doing anything with all the other mobs around, sorry. But if you see them doing the drain, a quick attack is all that is needed to break the action and have them target you, then it is just a regular elite fight.
One last thing, make sure everyone is ready and aware before the person with the blood goes to put the last torch out, because as soon as it is extinguished, the once ghost-form of the avatar hovering in the center of the room comes to life and starts pounding on the nearest target, so make sure your healer/ mages, or any other cloth wearers are well back. And this also gives you a chance to change the loot back to group loot before having to face the big guy (something I wish I had done) He drops some nice Rare BoP items, and it is kind of a bummer to have someone accidentally loot it without realizing it is still on free for all. Good luck and hope this makes the encounter a little easier for anyone else.

Once you use the egg in the room with hakkar's skeleton, the ghost of hakkar comes out with a few non-elite snakes.&nbsp Also spawning is an elite flying snake.&nbsp Kill the elite flying snake, and loot his blood.&nbsp Use the blood to put out one of the fires.

When you put out a fire, an elite summoner will spawn and start walking in.&nbsp Kill the elite summoner.&nbsp If you let him go, he will start shooting beams at the ghost of hakkar.&nbsp You do not want this to happen.&nbsp If you let them shoot the beams too long, hakkar will not summon and you have to reset the instance to do it again.

When you kill the summoner, another flying elite snake will spawn, which you have to kill to loot the blood.&nbsp Again use the blood on one of the fires, and repeat the same process.&nbsp Casters, you should drink in between fights to regen mana.&nbsp If you clear the two hallways leading to the room, its safe for a priest to use psychic scream if things get hairy.

When all four fires are out, hakkar will spawn, and then you kill him.&nbsp Loot the essence of hakkar off the body and use it from your inventory to complete the quest.&nbsp Turn in the quest back in steamwheedle.

Set your looting to "Free for All" to have 1 person gather the Bloods needed for the encounter. Once Hakkar is summoned, change it back to Master-Looter.

Ok here's how it works this is a more detailed description of the encounter than what the quest description says:

When someone has the egg they can use it in the Temple instance to "summon" Hakkar and start up the little event to summon him. When someone starts it both gates will close off the room, and Hakkar will spawn, but he's unkillable and he won't attack yet.

A couple non-elite snakes will spawn periodically throughout this event. They can easily be "round-up" by someone and then be killed by Area Effect spells. A few elite dragons will spawn also but again they're easily taken out if you have a good tank.

The important mobs you need to pay attention to is the Hakkar'i Bloodkeeper mobs that spawn. Once they're killed they drop "Hakkar'i Blood" regardless of what loot your group is set too someone needs to loot the blood and use it on one of the 4 "eternal flames" torches on 4 corners of the room. Once all 4 flames are put out the Avatar of Hakkar will spawn and you can attack him. Overall he's a pushover compared to the other bosses in this instance.

There is a belief pause between non-elite snakes and Hakkar'i Bloodkeeper so your casters can drink up and get mana back. Try to conserve mana.

Hope all this clears it up.

After you turned in the quest and talk to the NPC again, you can optional take another item.
He hints that you need to kill the avatar of Hakkar again.
I haven't done this part since it doesn't really appears to be a quest.
Does anyone know what's it about?
The item you get is: http://classicdb.ch/?item=10818

The suppressors are members of the Green Dragonflight trying to suppress Hakkar and keep him out of this world! If you don't kill the suppressors, they will dispell/despawn the "ghost-form" Hakkar before you can dowse all the flames and finish summoning it. Trying to use the egg again after that doesn't work. You have to reset the instance.

The despawn happened to my group between the third and fourth flame. Note that Hakkar was even more disappointed than us at this.

Therefore, you'd better kill those guys.

After each kill you loot the bodies and whoever loots the blood, needs to go put the flame out.&nbsp You have to do it 4 separate times.&nbsp After all the flames are gone, the boss spawns and you kill him.

Remember to click on the body and right click on the item in your inventory (to fill) to complete the quest.