WoWDB

 Bloody Coin is a PvP currency actually. Get your  Censer of Eternal Agony from the vendor Speaker Gulan and start killing people around (you can use this item only on Timeless Isle). You'll get Bloody Coins for any people you kill under the effect. Said vendor has a list of available rewards for the Bloody Coin, such like battle pet and mount!

Currently, you only generate  Bloody Coins for killing blows, not regular HKs which can make them really difficult to farm for some classes.

Undocumented hotfix: Censer of Eternal Agony now costs 1,000 x Timeless Coins, down from 2,500.

you have to heal up after use - its a protection that you "can't surprise" people ;)

You cannot earn reputation with Emperor Shaohao while under the effects of this.

This makes sense - I don't think Shaohao would approve of a person using an Ordon relic to gank other people - but I'm still sad. No trying for any of the censer-related achievements until I hit Exalted with his reputation.

Stealth-hotfixed on June 11, 2014. Now has a cooldown of 1 hour, up from 10 minutes.

For more information: Recent Bloody Coins Hotfixes