WoW Classic Zul’Gurub reset time is three days. This means that once every 72 hours the bosses you killed will respawn.
There’s no attunement quest. Unlike the other three raids before it, Zul’Gurub does not require you tp complete lengthy quest-chains. You just enter the portal like you would for a dungeon.
In theory, you can rush to the end boss. You don’t need to kill all the bosses before the final boss. You can just go and engage the last boss, Hakkar, while the High Priests are still alive, but you will most likely fail. Each Priest empowers Hakkar with a buff and it’s extremely challenging to kill him while he has all five buffs. However, it’s not impossible. Such a kill has already been claimed in WoW Classic. No one managed this achievement in Vanilla.
Ignore the adds for the High Priest Arlokk fight. This probably goes against what you hear most of the times, but focus on burning the boss while it is active. Switch to the adds when the boss vanishes.
Position High Priest Jek’lik on the hill. On the right side of the boss area, there is a small hill. Position the boss there to have more room during the fight.
Interrupt High Priest Mar’li when healing. Watch out for the boss’s Drain Life spell. It will heal it and damage the target. Luckily, you can and should interrupt it. Set up an interrupt rotation if needed.
Kill High Priest Thekal’s adds at the same time. You will be fighting three adds in the first phase. All three of them must die at the same time.
Dispel High Priest Venoxis. The boss uses Renew which heals it. Classes with dispelling abilities such as priests and shamans can use their spells to remove Renew from the boss.
Get the debuff when fighting Hakkar. The Poisonous Blood debuff is essential to this fight. Make sure you have it when the boss Blood Siphons. If you don’t have the debuff, you will help the boss gain HP.
Don’t die too many times during the Bloodlord Mandokir fight. The good news is that you get resurrected if you die during the fight. The bad news is that each death buffs the boss.
Focus the adds, not Jin’do. When fighting this boss, it is important to keep in mind that adds take priority. Don’t touch the boss if there are adds still up.
(Contributed by Reda; Edited by Hermes_Fang)