If you hope to get the rare Deathcharger's Reins mount from Baron Rivendare for example, we know that it has a 1% drop chance. That means that every time you kill the Black Baron you have a 1% chance of getting the mount. 1% on the first kill, and 1% on the 100th kill. However, over the course of 100 kills, you have a much higher probability of getting the mount. But not 100%. Never 100%.
