Prophet Khar'zul

In case you're unsure, Mishi will take you to the Isle of Reckoning. Mishi can be found to the right, outside of the building that Lorewalker Cho is in.

Mishi will also return you when you are done with the Prophet. She will be down the stairs from the altar, to the left.

For the Cauldrons found on the isle
Purple: Summons maggots, makes you purple and vomit for 2 minutes
Blue: Makes all the trolls on the island passive (still attackable)
Red: A well fed buff for 100 Mastery
Green: 2 minute buff that gives you a chance on hit Hex spell. Doesn't break with damage, no apparent diminishing returns.

Interesting to note, the Blue cauldron buff will make players of the opposite faction friendly and unattackable, so long as they have the buff as well. Enemy players can exchange buffs and the like, although the language barrier still exists.
/dance emote used on the Witchdoctors will yield the line "I be jammon wit' you, <name>"

The cauldrons with the blue light over them are the ones that will give you a disguise that will make all the mobs neutral, except for Prophet Khar'zul, your disguise will disappear when you approach him.

After you kill him Mishi is at the bottom of the stairs, don't fight your way back to the entrance like I did, lol.

Did this again today on an alt, just want to add 1 more thing to it. After you kill Prophet Khar'zul, if you have not yet killed the requisite number of Gurubashi Mishi will not be where he should be. Go and kill the 12 you need then go back up the stairs where Prophet Khar'zul is, (don't pull him, not necessary to kill him again) then just walk back down and Mishi will have spawned.