You don't have that yet? What are you missing?
Mounts are account-wide, but not for achievements (exceptions are some of the garrison stuff). You can have some characters with achievements others don't, but they don't intersect for raiding.
If you don't get it tonight, contact me after reset, I've banged out every achievement there. I only had a problem with the green dragon because of portal jockey and healing, but need a reset to finish that up (I fucked up between 10 and 25 instances with my priest).