The Black Prince is a faction in Pandaria consisting of Wrathion and his underlings. The quest rewards from this faction are impressive such as legendary gems with +500 agility or +500 strength or +500 intellect.
Beware though, some of these gems only fit in Sha-touched sockets. And these sockets are only found on weapons from Grand Empress Shek’zeer in Heart of Fear and Tsulong, Lei Shi and Sha of Fear in Terrace of Endless Spring. Other legendary gems do fit in any sockets.
Now, until revered, you can get reputation by killing level 90 mogu and mantid. From revered to exalted, you will get reputation by killing opposing faction in Krasrang Wilds and most mobs on the Isle of Thunder. From Revered to Exalted, only mobs from Isle of Thunder will count (and then quests, of course).
Now this trick is to pull you from Neutral to Revered in about half an hour.
It is pretty simple: Go to Townlong Steppes, west, on the island right west of the steppes.
There, you will see a place called Niuzao Temple.
In this temple, there are many, many, many mantids and some guards.
All you have to do is to get there, tag or aggro a bunch of mantids and then run back to the guards. The guards will take care of the mobs for you while you can run out and aggro some more. Remember to dot, hit or aoe the mobs to be sure to tag them, then you will get reputation and very good loot (even better if you use a potion of luck).
In about 30 minutes, you should be revered.