Just a friendly PSA: if you want the Demonslayer title you might want to start now as one of the requirements is to kill non trivial demons in Argus and who knows how this will be impacted come Shadowlands.
If you already have it, congratulations disregard this message. 
5000 non-trivial demon kills in any of the 3 Argus zones if youâre not sure what sheâs referencing.
it would be such a silly title for a demon hunter. Demonslayer Demon Hunter Demon Enthusiast
Best place to farm I find is right at the start of all the quests there
Handful of NPCs stand there and mobs donât stop spawning and rushing there
Good luck
The content will be 15 levels below max with the Shadowlands rework.
If you arenât one shotting them, itâs a bug, report it, and it will be fixed.
Thatâs part of the problem though, greys donât count based on the achievement wording
I forsee a lot of bugs, but thankfully I have this title. It took awhile because I kept getting tired of doing it and leaving, I think it was something like first time to 800, second time to like 2000 and the third time I went I put on music, was determined and sat there killing demons from 2k to 5k. Was happy when it was over, lol.
Probably goes faster with friends or guildmates, but alas I didnât really have any soâŚyeah. 
Quite the contrary; I prefer it to âSlayerâ as itâs more specific as to what I am a slayer of. Demonslayer Ashnazg.
As soon as I saw this title was available, I went out of my way to get it and have not used another title since.
My demon hunter is proud trashmaster
Que the âRip and Tearâ from Doom lol
I donât think itâs based on level. I think it just means the âlesserâ mobs donât count (donât know what you call them, but the type of mob that has a different display on your UI when you click on them).
I forgot this was even a thing. I spent a lot of time on argus with my war. Need to check and see what his progress is when I get home.
Thereâs also a mount reward at 2k demon kills