Bloody Coins is a PvP currency added in patch 5.4, which lets you buy a mushan mount (Reins of the Ashhide Mushan Beast) and a porcupine pet (Vengeful Porcupette). In order to get Bloody Coins, you need to purchase the item Fire-Watcher's Oath from Speaker Gulan on the Timeless Isle in Pandaria. This item costs 100 Timeless Coins (which you should be able to get by killing a few rares on the island if you don't already have then). If you use the item, you will get one Bloody Coin every time you kill an enemy of the other faction.
The mechanics behind the item pretty much lets you get coins when you kill other players, but in this guide you will learn how to farm all the Bloody Coins needed for the mount and pet very fast, without even having to be good at PvP. The trick is to use the portal to Hyjal and fly to the enterance to Firelands (the raid). This spot will be full of botters who don't really fight back, so just use the Fire-Watcher's Oath and have fun killing them over and over. Most servers will let you be able to get the mount within 30 minutes! The Reins of the Ashhide Mushan Beast costs a total of 500 Bloody Coins, but with this method is should be really fast to get.