The Ninth Boss
Strategy
Majordomo Executus is one of the only bosses in WoW Classic that shouldn't be focused throughout the fight, with the best plan of action being to constantly tank him with one or two players instead. In addition to his conventional arsenal of spells, Executus will Teleport the tank with the highest threat. This will reset their threat entirely, so you should have a second tank on hand to engage the boss and pick up the aggro straightaway.
Executus is accompanied by four Healers, who should be Polymorphed, and four Elites, who should be tanked. There are two main spells to be aware of, both of which may kill a significant portion of your raid if you're not careful. The first, Damage Shield, will reflect physical damage back to your Melee classes, and the second, Magic Reflection, will do the same, but for magic damage to your Casters. Depending on which buff is active, physical or magic, classes dealing that kind of damage should disengage from the boss for the duration of the spell. In addition, the magic barrier also reflects the effects of Polymorph, so make sure the buff has faded before your mages try to sheep the mobs.
Make sure that your raid stays away from the adds throughout the fight to avoid taking damage from Fire Nova.
First of all, you should focus on two of the four Flamewalker Elites. Once they've been defeated, damage the remaining two until they both have around 25% HP remaining. Once you've completed that step, focus on two of the Healers, then finish of the two remaining Elites before finally killing the last two Healers. Once all of accompanying mobs are dead, the fight will finish and Executus will disappear, leaving behind a lootable chest.