Playing through the Warlords of Draenor alpha, it quickly becomes apparent that the Timeless Isle was a preview of the upcoming expansion's world design. While quests and quest hubs are still present in spades, the game world is littered with bonuses -- hidden caches of materials for your garrison, rare spawns, and little stories in out-of-the-way places. While questing through Frostfire Ridge, I saw a skull on my minimap in the region known as the Boneslag. Assuming it was another rare spawn of many, I rushed down and encountered Cindermaw. I didn't know it at the time, but Cindermaw isn't a standard rare spawn at all. He's something Blizzard is calling a vignette.
I was able to solo Cindermaw, and quite easily at that, but the encounter was more involved than I'd expected. After beating on him for awhile, he burrowed underground and I was given a warning that he'd moved to the southeast. A few moments later, he reappeared far out of the standard combat range, where a normal mob would leash and reset. Instead, I remained in combat with the worm, needing to pursue him through the Boneslag, fighting through (or attempting to avoid) all of the orcs that stood between us. I reached him and managed to do only a little more damage before he burrowed again, causing me to pursue once more. On the third engagement, I used my cooldowns to kill him before he could flee any further. My efforts were rewarded with Cindermaw's Blazing Talon.
Vignettes appear to bring a more dynamic type of encounter to the game world, something more akin to a dungeon boss than the typical overworld monster. Cindermaw was my first kill towards the achievement The Frostwind Slayer, which lists eight different vignettes in Frostwind Desert -- what I assume to be a deprecated name for Frostfire Ridge. If that's correct, it's safe to assume every zone in Draenor will have its own set of vignettes.