The Whiplash rare World Quest is back! One step closer to the 
Jani’s Trashpile mount, the quest brings with it, well, Whiplash, the rare needed to complete the 
Adventurer of Stormsong Valley meta-achievement, which is itself needed for the 
A Farewell to Arms meta for Battle for Azeroth, which grants the Jani full transformation mount. It’s up for another 9ish hours as of this post, so be fast.
As suggested by the achievement, head on over to Stormsong Valley, go south of the Brennadam windmill, and into Briarback Kraul. Whiplash is at 47.2, 65.8.
There’s nothing special to do to get the credit, just kill the rare in the cave.
Good luck with the rest of your Jani hunt, and here’s a video showing where to find the rare.