I’ve been farming for about 5 years for the drake from Deathwing for the Awake the Drakes achievement. I started before the achievement even came into the game. I had seen it was coming on the beta.
I usually only do one kill a week though as I can never be bothered farming on multiple alts. So far the rest of my runs have dwindled to a handful after having more luck with other mounts. I just don’t seem to have any luck with that particular mount.
Invincible, seems is invisible 
, so i gave up.
Most recent longest was Shackled Ur’zol. I’ve farmed it from the 2nd week of BFA till the day 8.2 came out. Gotten pretty lucky with the other mounts though got Invincible on the 4th run. Same with Ravenlord and Karazhan mounts.
But the longest was Ashes of Al’ar and Mimiron’s head. Both Took me 4 years.
[WHAT’S THE LONGEST TIME YOU’VE SPENT FARMING AMOUNT]
anything? everything? since 2007. and most of it still hasn’t dropped for me. ashes, mimirons head, invincible, zg raptor, ultraxion mount, pandaland world boss mounts, etc etc etc still all greyed out 
having a drop rate like this is just wrong. its sadistic and abusive and no collector in their right mind would advocate for it without ulterior motive.
maybe reason to petition better drop rates on mounts, pets, toys and transmog?
i have a spare reins of the raven lord on an alt if you want a swap… … … …
I think Im lucky so far Elegon mount( on 3rd kill ) Swift Zulian Panther ( on 1st kill ) , drake from EoA ( like 2nd kill) and got Ji Kun mount like 5 hours ago ( i think it was 5th or 6th kill) i dont even have achiv for 50 mounts I think i got super lucky but most farmed one for me so far was LK mount ( 11 kills) Hope i get it today
Tusks .
Tusks of mannaroth all day all night :’)
invincible. since the 1st time ive beaten arthas in wotlk times. still no drop
I remember getting mine in a call to arms bag I got from tanking some random dungeon. I wonder if those bags still drop dungeon mounts? 
In contrast to all these mount we work hard for, but never get. Let me tell you of the two annoying mount-drops I have had. 
When Noblegarden was first introduced, I went to the event having in mind to farm eggs for the mount. I was all set up with snacks and all for this long grind…
My second egg contained the mount 
Druing the Halloween event, I went E-V-E-R-Y day, on every char I had for the first couple of years, into the dungeon in the hopes of getting lucky with the mount. I never got it of cause.
I did so too on the Third year, though the last day of the event I had enough. “Fu*k it… I’ll never get it anyways” and decided that enough was enough. Moments later my friend asked if I could tank the dungeon, just once, for him to get fast queue. I didn’t want to but did it anyways, after he talked me into it… and what was in my loot… The effin horse
Today these are my least used mounts, and I still glare at them when I see them in the tab haha.
Blackhand-456 kills still no mount
Sha-almost 1100 kills
But got galleon,oon and nalak at least
Two days for me, the Baron mount from Stratholme. Must have been the longest one. I never really cared about farming mounts and transmogs and pets and whatnot, least of all achievements.
One sentence, “Its been a long strange Trip”.
Literally took me 10 years.
For me it will be “Voidtalon of the Dark Star”, almost every day i was flying and looking for portals ever since i earned flying in draenor and i got mount late in legion.
Try the world boss mounts of pandaria. people have been hunting them for years, and thanks to their 1/2000 drop chances, GOODLUCK getting them. 3 months? I don’t remember a rare mount taking me less time.
I was farming for Ashes of Al’ar from late WotLK till mid-Legion. So that’s… 2009-2017, a total of eight years give or take a bit. The last mount I need for the Emerald Drake achievement is the Blazing Drake from Deathwing - guess how long I’ve been farming that? And to get it, I’ve got to listen to all that damn monologing from the Aspects AND the Spine of Deathwing fight.
I hate the Spine of Deathwing.
Been farming Sha of Anger since MoP. Probably will never see that mount, but it’s good to vent out my anger on that guy. (get it?)
About 1,5 years (77 runs) worth of lockouts for the last Glaive of Azzinoth on my Rogue. This is one of those farms that has to be done on that one char so I have only done one run pr week.
It’s not as many individual runs, but since I am limited to that one char, it takes alot longer. Still running BT for it.
I did 269 runs for the Deathcharger on this char, but I didn’t spend as long RL time since I was able to run up to 10 (or 5? I can’t remember if it was changed at that point) runs pr hour. This was before mounts were account-wide.
about Glaive of Azzinoth, your thinking is incorrect, i had one glaive for years on my main, never get other one, started to farm on all classes that can collect it and was lucky to get both of them one week after another on other character, while main has still one of them only. I assumed here that like myself you are collecting them to unlock look on your demon hunter, because obviously if not and you just want both on your rogue then my suggestion is useless
Can i just hate you. Took me ToT to last week for Horridon, and the bloody bird drives me insane.
Your banes however I have got all. TW mount I got from 2nd boss kill on the patch it came, Startholme total was eventually 1062 runs (they rose % in wotlk, in which were I got it with 72 additional kills from 900+ I did inTBC and I got it from the LFG bonus bag - as then those bags had chance to drop mounts) Ultraxxion mount i got when we raided the place. Got all DS mounts when we raided it.
But no Throne of Thunder drives me insane by now. INSANE. INSANE
Good luck, honestly. This stubborness you must have !
3 months try 1200+ kills for mims head and still counting .
Over 2k kills for sha . 3 months is nothing . I know people on 15k + for TW mount still.