The order in which you do the bosses doesn't really matter; I've just organized them here by the most conventional route through the instance. Some of the trash in Zul'Gurub is legitimately dangerous to an unprepared group, so I've included notes on how to handle it.
After you zone into the instance, you'll notice a foggy path in front of you with a single caster add channeling from a cauldron.
The cauldron, once clicked, provides a buff decreasing nature damage taken by 90% for about 25 seconds. What's the catch? You can't click it until the mob next to it has died.
Before you get the cauldron buffs, the associated NPC will randomly select targets for about 6-7K damage per second attack. It's healable but not fun. Once you've got the cauldron buff, the damage from the green fog along the path is negligible.
The two most important mob abilities -- and things you'll see in the Venoxis encounter -- are as follows:
A green line will sprout between two random players in the group and do damage each second to both them and anyone else they're around. Run away from the person to whom you're linked, because staying on top of a linked player hugely
increases the damage. If you're tanking or doing melee DPS, be very careful if another melee player gets linked to you and doesn't run away. Ranged DPS should try to spread out as much as possible.
Breath of Hethiss
You'll see this fun little ability trotted out by the two snake adds directly before pulling Venoxis. It's a frontal cone AoE that does enormous damage (to the tune of 26,000-27,000 per second) with both mobs often performing it at once. Pull these adds back to the nature resistance cauldron outside Venoxis' enclosure, and don't forget to rebuff yourself continually.
High Priest Venoxis ("snake boss")
The one thing you have to know about this fight: If it's green, it's mean. In addition to Toxic Link and Breath of Hethiss, Venoxis will also put a maze of poison lines on the ground and spend portions of the fight channeling three beams that will chase people.
If you're tanking Avoid green stuff on the ground, watch out for Toxic Link, interrupt his channeled attack (it looks like a green version of the discipline priest's Penance), and be prepared to pop some cooldowns if your healer's on the run. However, your most important responsibility here to is to keep Venoxis turned away from the group and to run the hell out of the Breath of Hethiss attack, which is still a frontal cone AoE. However, here it's a frontal cone AoE without the 90% nature damage reduction buff from a cauldron. This can get tricky, given the poison maze on the ground, so have a workable escape route before it happens. If you've got a choice between running over a poison line on the ground or swallowing a Breath tick, take the former. Also, turning Venoxis into the rest of the group while he's channeling the Breath is not the best idea ever.
If you're healing The opportunities for sudden damage on this fight are plentiful, especially if people aren't smart about Toxic Link. The most dangerous portion of the fight with respect to group healing will occur as three beams chase players around the maze of poison Venoxis has created. If it comes down to swallowing a beam or swallowing damage from going over a poison line, encourage people to do the latter; crossing a poison line is only about 14,000 damage, but taking a beam is more than twice that. The difference between an experienced and not-so-experienced group on this fight is huge.
If you're DPSing Avoid bad stuff, avoid bad stuff, and avoid bad stuff. If you're ranged, stay spread out as much as possible to decrease the danger from Toxic Link. After Venoxis finishes channeling the three poison beams, he becomes "exhausted," parks himself at the top of his little platform, and takes a huge amount of damage. Save your big damage cooldowns for this, and his health should drop like a stone.
Proceeding up the hill from Venoxis' enclosure will send you toward Bloodlord Mandokir (the raptor boss). On the steep hill immediately before Mandokir's enclosure, you'll have to avoid a series of rocks being rolled downhill. If you get hit, they'll toss you back with about 30,000 damage, which I totally took on purpose for the sake of this article and Science™ (right). This is problematic if you're healing and get belted out of range of an oblivious tank, so don't be
bad. Avoiding the rocks is generally easy as long as you're paying attention.
Trash is otherwise unremarkable, although this time the associated cauldron (frost) gives you a buff that freezes mobs once they're hit. This comes in handy if your crowd control is spotty (or otherwise unreliable). Don't forget what the frost cauldron does, by the way; you'll be seeing it again on a future boss. However, you do not need the cauldron buff for Mandokir.
Bloodlord Mandokir ("raptor boss")
Fans of the original Zul'Gurub will be pleased to hear that he still levels up with a "Ding!" (and distant reply of "Grats!") when he kills a player. Players getting killed is actually a standard part of the encounter, so don't freak out if you're healing. Eight ghostly troll priests around Mandokir's enclosure will resurrect fallen players, and Mandokir's "leveling up" is a built-in DPS check. With each level that he gains, his damage increases, so ... yeah. The general idea is to kill him before he's capable of two-shotting your tank and you run out of priests to resurrect players. The latter is complicated by Mandokir's raptor, Ohgan, who will kill the priests if left to his own devices and is eventually resurrected by Mandokir after players kill him.
If you do nothing else on this encounter: Kill the raptor. Kill the raptor. And then kill the raptor some more. Mandokir's only other ability of note is a telegraphed attack called Devastating Slam, which is heralded by a series of spikes and a red glow on the ground before it lands. If your group can stay out of this, switches to the raptor promptly, and has decent DPS, this is a pretty easy fight.
If you're tanking Mandokir will start the fight mounted on Ohgan. Tank him in the center of the enclosure to start. Before long, Mandokir will hop off, and the raptor will become a separate mob. Ohgan can't be tanked, but you can help put some extra damage on him and keep debuffs up. Assuming your DPS is paying attention, the raptor should die well before he reaches and kills a priest. When Ohgan dies, tank Mandokir on top of his corpse so you and melee DPS can reach him immediately once he's resurrected. You're immune to Mandokir's one-shot random kill, but your healer is not -- and Mandokir's damage will keep going up as the fight goes on. Keep your cooldowns for the latter half of the fight.
If you're healing You are not immune to Mandokir's one-shot random kill attack, so be prepared to blow a cooldown or two if you die at an inconvenient time. However, this is definitely an easier fight to heal than Venoxis. Ignore the random deaths, stay out of Devastating Slam, and if you've got some free time, help put some damage on Mandokir/Ohgan. I found healing requirements to be fairly light here, particularly in the early portion of the fight.
If you're DPSing This fight is a DPS race; if you can't kill Mandokir before the eight ghostly priests are killed or else "used up," Mandokir wins. Stay out of Slam, switch to Ohgan as soon as he's resurrected, and just keep unloading on Mandokir.